diff --git a/mindspore/ccsrc/minddata/dataset/api/datasets.cc b/mindspore/ccsrc/minddata/dataset/api/datasets.cc
index eed410f22a9..97c1b4d7c42 100644
--- a/mindspore/ccsrc/minddata/dataset/api/datasets.cc
+++ b/mindspore/ccsrc/minddata/dataset/api/datasets.cc
@@ -556,8 +556,8 @@ std::shared_ptr<SentencePieceVocab> Dataset::BuildSentencePieceVocab(
   const std::vector<std::string> &col_names, uint32_t vocab_size, float character_coverage,
   SentencePieceModel model_type, const std::unordered_map<std::string, std::string> &params) {
   auto vocab = std::make_shared<SentencePieceVocab>();
-  auto ds = std::make_shared<BuildSentenceVocabNode>(IRNode()->DeepCopy(), vocab, col_names, vocab_size,
-                                                     character_coverage, model_type, params);
+  auto ds = std::make_shared<BuildSentenceVocabNode>(IRNode(), vocab, col_names, vocab_size, character_coverage,
+                                                     model_type, params);
 
   std::unique_ptr<NativeRuntimeContext> runtime_context = std::make_unique<NativeRuntimeContext>();
   Status rc = runtime_context->Init();
@@ -588,8 +588,8 @@ std::shared_ptr<Vocab> Dataset::BuildVocab(const std::vector<std::string> &colum
                                            const std::pair<int64_t, int64_t> &freq_range, int64_t top_k,
                                            const std::vector<std::string> &special_tokens, bool special_first) {
   auto vocab = std::make_shared<Vocab>();
-  auto ds = std::make_shared<BuildVocabNode>(IRNode()->DeepCopy(), vocab, columns, freq_range, top_k, special_tokens,
-                                             special_first);
+  auto ds =
+    std::make_shared<BuildVocabNode>(IRNode(), vocab, columns, freq_range, top_k, special_tokens, special_first);
 
   std::unique_ptr<NativeRuntimeContext> runtime_context = std::make_unique<NativeRuntimeContext>();
   Status rc = runtime_context->Init();
diff --git a/mindspore/ccsrc/minddata/dataset/engine/datasetops/dataset_op.cc b/mindspore/ccsrc/minddata/dataset/engine/datasetops/dataset_op.cc
index 0e9d9aa977d..c1b42bf935c 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/datasetops/dataset_op.cc
+++ b/mindspore/ccsrc/minddata/dataset/engine/datasetops/dataset_op.cc
@@ -206,9 +206,6 @@ void DatasetOp::Parent(DatasetOp **parent, int32_t parent_index) const {
   }
 }
 
-// Getter function to get all of our children.
-std::vector<std::shared_ptr<DatasetOp>> DatasetOp::children() const { return child_; }
-
 // Getter function to get all of our parents.
 std::vector<DatasetOp *> DatasetOp::parents() const { return parent_; }
 
diff --git a/mindspore/ccsrc/minddata/dataset/engine/datasetops/dataset_op.h b/mindspore/ccsrc/minddata/dataset/engine/datasetops/dataset_op.h
index 39ab602fe9a..811cb7ff087 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/datasetops/dataset_op.h
+++ b/mindspore/ccsrc/minddata/dataset/engine/datasetops/dataset_op.h
@@ -111,9 +111,6 @@ class DatasetOp : public std::enable_shared_from_this<DatasetOp> {
   /// \param[in] parent_index An operator can have n parents. Indicates which parent to return.
   void Parent(DatasetOp **parent, int32_t parent_index) const;
 
-  // Getter function to get all of our children.
-  std::vector<std::shared_ptr<DatasetOp>> children() const;
-
   // Getter function to get all of our parents.
   std::vector<DatasetOp *> parents() const;
 
diff --git a/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/dataset_node.cc b/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/dataset_node.cc
index 1a314858d42..f9164723928 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/dataset_node.cc
+++ b/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/dataset_node.cc
@@ -233,40 +233,14 @@ std::shared_ptr<DatasetNode> DatasetNode::SetNumWorkers(int32_t num_workers) {
   return shared_from_this();
 }
 
-DatasetNode::DatasetNode() : cache_(nullptr), parent_({}), children_({}) {
+DatasetNode::DatasetNode() : cache_(nullptr), parent_(nullptr), children_({}) {
   // Fetch some default value from config manager
   std::shared_ptr<ConfigManager> cfg = GlobalContext::config_manager();
   num_workers_ = cfg->num_parallel_workers();
   rows_per_buffer_ = cfg->rows_per_buffer();
   connector_que_size_ = cfg->op_connector_size();
   worker_connector_size_ = cfg->worker_connector_size();
-}
-
-const bool DatasetNode::IsTree() const {
-  bool is_tree = true;
-  if (this->parent_.size() > 1) {
-    MS_LOG(WARNING) << Name() << " has more than one parent.";
-    return false;
-  }
-  for (const auto &child : children_) {
-    is_tree = child->IsTree();
-    if (!is_tree) {
-      MS_LOG(WARNING) << Name() << " has more than one parent.";
-      break;
-    }
-  }
-  return is_tree;
-}
-
-// this function will preform a deep copy of current node (and its descendants), the parent* pointer will not be copied
-std::shared_ptr<DatasetNode> DatasetNode::DeepCopy() {
-  std::shared_ptr<DatasetNode> new_node = this->Copy();
-  // temporary fix to set the num_workers to the new node.
-  new_node->SetNumWorkers(this->num_workers_);
-  for (const auto &child : children_) {
-    new_node->AddChild(child->DeepCopy());
-  }
-  return new_node;
+  mappable_ = kNotADataSource;
 }
 
 std::string DatasetNode::PrintColumns(const std::vector<std::string> &columns) const {
@@ -310,54 +284,105 @@ void DatasetNode::PrintNode(std::ostream &out, int *level) const {
 }
 
 // Add a node as a child, node's parent needs to be empty
-// this function will allow child to be a nullptr, in which case it will simply skip
+// This function will allow child to be a nullptr, in which case it will simply skip.
+// This function is used only when building IR node one by one from parsing the user code.
+// During the parsing, we allow a node to have more than one parent, possibly forming a graph.
+// It does not maintain the parent_ attribute of the node, which enforces a single parent and a tree structure.
 void DatasetNode::AddChild(std::shared_ptr<DatasetNode> child) {
-  if (child != nullptr && child->parent_.empty()) {
+  if (child != nullptr) {
     children_.push_back(child);
-    child->parent_.push_back(this);
-  } else if (child != nullptr) {
-    MS_LOG(WARNING) << "Adding " + child->Name() + " to " + Name() + " but it already has a parent";
-    children_.push_back(child);
-    child->parent_.push_back(this);
   }
 }
 
-// Insert a node as a child of this node. This node's children becomes the children of the inserted node.
+// Add the input node to be the next child of this node
+// This function is used in doing a deep copy of the IR tree built by parsing the user code.
+// This function assumes we walk the tree in DFS left-to-right.
+// This is a temporary function to be replaced later by a set of better tree operations.
+void DatasetNode::AppendChild(std::shared_ptr<DatasetNode> child) {
+  if (child != nullptr) {
+    if (child->parent_ != nullptr) {
+      MS_LOG(WARNING) << "Adding " + child->Name() + " to " + Name() + " but it already has a parent";
+    }
+    children_.push_back(child);
+    child->parent_ = this;
+  }
+}
+
+// Add a node as a parent, node's parent needs to be empty (future use)
+Status DatasetNode::InsertAbove(std::shared_ptr<DatasetNode> node) {
+  CHECK_FAIL_RETURN_UNEXPECTED(node != nullptr, "Inserted node must not be a null pointer.");
+
+  if (node->parent_ != nullptr) {
+    DatasetNode *parent = node->parent_;
+    for (auto i = parent->children_.size() - 1; i >= 0; --i) {
+      if (parent->children_[i] == node) {
+        parent->children_[i] = static_cast<std::shared_ptr<DatasetNode>>(this);
+      }
+    }
+  }
+  children_.push_back(node);
+  node->parent_ = this;
+
+  return Status::OK();
+}
+
+// Insert a node as a child of this node
+// This node's children become the children of the inserted node.
 Status DatasetNode::InsertBelow(std::shared_ptr<DatasetNode> node) {
   CHECK_FAIL_RETURN_UNEXPECTED(node != nullptr, "Inserted node must not be a null pointer.");
   CHECK_FAIL_RETURN_UNEXPECTED(node->children_.empty(), "Inserted node must not have any children.");
-  CHECK_FAIL_RETURN_UNEXPECTED(node->parent_.empty(), "Inserted node must not have a parent.");
+  CHECK_FAIL_RETURN_UNEXPECTED(node->parent_ == nullptr, "Inserted node must not have a parent.");
 
   for (auto child : children_) {
     node->children_.push_back(child);
-    child->parent_.clear();
-    child->parent_.push_back(node.get());
+    child->parent_ = node.get();
   }
   // Then establish the new parent-child relationship with the new parent.
   children_.clear();
   children_.push_back(node);
-  node->parent_.clear();
-  node->parent_.push_back(this);
+  node->parent_ = this;
+  return Status::OK();
+}
+
+// Insert a node as a child next to this node (future use)
+Status DatasetNode::InsertAfter(std::shared_ptr<DatasetNode> node) {
+  CHECK_FAIL_RETURN_UNEXPECTED(parent_ != nullptr, "This node must have a parent.");
+  CHECK_FAIL_RETURN_UNEXPECTED(node->parent_ == nullptr, "Inserted node must not have a parent.");
+  auto size = parent_->children_.size();
+  // Duplicate the last child to increase the size by 1
+  parent_->children_.push_back(parent_->children_[size - 1]);
+  // Shift each child to its right until we found the insertion point, then insert the input node
+  bool found = false;
+  for (auto i = parent_->children_.size() - 2; i >= 0; --i) {
+    if (parent_->children_[i].get() != this) {
+      parent_->children_[i + 1] = parent_->children_[i];
+    } else {
+      parent_->children_[i + 1] = node;
+      node->parent_ = parent_;
+      found = true;
+      break;
+    }
+  }
+  CHECK_FAIL_RETURN_UNEXPECTED(!found, "Insertion point not found.");
   return Status::OK();
 }
 
 // Remove this node from its parent. Add the child of this node to its parent.
 // for now, this remove is limited to node with a single child or no child
 Status DatasetNode::Remove() {
-  CHECK_FAIL_RETURN_UNEXPECTED(parent_.size() != 0, "Cannot remove root or a node without parent.");
+  CHECK_FAIL_RETURN_UNEXPECTED(parent_ != nullptr, "Cannot remove root or a node without parent.");
   CHECK_FAIL_RETURN_UNEXPECTED(children_.size() < 2, "Cannot remove node with more than 1 child.");
   if (children_.empty()) {  // I am a leaf node, remove me from my parent's children list
-    parent_[0]->children_.erase(
-      std::remove(parent_[0]->children_.begin(), parent_[0]->children_.end(), shared_from_this()),
-      parent_[0]->children_.end());  // removal using "erase remove idiom"
-  } else {                           // replace my position in my parent's children list with my single child
-    auto itr = std::find(parent_[0]->children_.begin(), parent_[0]->children_.end(), shared_from_this());
-    CHECK_FAIL_RETURN_UNEXPECTED(itr != parent_[0]->children_.end(), "I am not in my parent's children list.");
+    parent_->children_.erase(std::remove(parent_->children_.begin(), parent_->children_.end(), shared_from_this()),
+                             parent_->children_.end());  // removal using "erase remove idiom"
+  } else {  // replace my position in my parent's children list with my single child
+    auto itr = std::find(parent_->children_.begin(), parent_->children_.end(), shared_from_this());
+    CHECK_FAIL_RETURN_UNEXPECTED(itr != parent_->children_.end(), "I am not in my parent's children list.");
     children_[0]->parent_ = parent_;  // set my single child's parent ptr to my parent
     *itr = std::move(children_[0]);   // replace me in my parent's children list with my single child
-    children_.clear();                //  release my single child from my children list
+    children_.clear();                // release my single child from my children list
   }
-  parent_[0] = nullptr;
+  parent_ = nullptr;
   return Status::OK();
 }
 
diff --git a/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/dataset_node.h b/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/dataset_node.h
index f037a460ba8..a2480b65d6f 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/dataset_node.h
+++ b/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/dataset_node.h
@@ -146,10 +146,6 @@ class DatasetNode : public std::enable_shared_from_this<DatasetNode> {
     return out;
   }
 
-  /// \brief Make a new copy of the tree from the current node
-  /// \return The new copy of the tree
-  std::shared_ptr<DatasetNode> DeepCopy();
-
   /// \brief Pure virtual function to convert a DatasetNode class into a runtime dataset object
   /// \param node_ops - A vector containing shared pointer to the Dataset Ops that this object will create
   /// \return Status Status::OK() if build successfully
@@ -175,43 +171,61 @@ class DatasetNode : public std::enable_shared_from_this<DatasetNode> {
   /// \return Child nodes
   const std::vector<std::shared_ptr<DatasetNode>> Children() const { return children_; }
 
-  /// \brief Getter function for parents nodes
-  /// \return Parent nodes
-  const std::vector<DatasetNode *> Parent() const { return parent_; }
+  /// \brief Getter function for the parent node
+  /// \return The parent node (of a node from a cloned IR tree)
+  DatasetNode *Parent() const { return parent_; }
 
-  /// \brief Establish the parent-child relationship between this node and its child.
+  /// \brief Establish a parent-child relationship between this node and the input node.
+  ///    Used when building the IR tree.
   void AddChild(std::shared_ptr<DatasetNode> child);
 
+  /// \brief Establish a parent-child relationship between this node and the input node.
+  ///    Used during the cloning of the user-input IR tree (temporary use)
+  void AppendChild(std::shared_ptr<DatasetNode> child);
+
+  /// \brief Establish the child-parent relationship between this node and the input node (future use)
+  Status InsertAbove(std::shared_ptr<DatasetNode> node);
+
   /// \brief Insert the input node below this node. This node's children becomes the children of the inserted node.
   Status InsertBelow(std::shared_ptr<DatasetNode> node);
 
+  /// \brief Add the input node as the next sibling (future use)
+  Status InsertAfter(std::shared_ptr<DatasetNode> node);
+
   /// \brief detach this node from its parent, add its child (if any) to its parent
   /// \return error code, return error if node has more than 1 children
   Status Remove();
 
-  /// \brief  Check if this node has cache
+  /// \brief Check if this node has cache
   /// \return True if the data of this node will be cached
   const bool IsCached() const { return (cache_ != nullptr); }
 
-  /// \brief  Check if this node is a tree
-  /// \return True if the structure is indeed a tree, i.e., no node has more than one parent
-  const bool IsTree() const;
-
-  /// \brief  Check if this node is a leaf node.
+  /// \brief Check if this node is a leaf node.
   /// \return True if this is a leaf node.
   const bool IsLeaf() const { return children_.empty(); }
 
-  /// \brief  Check if this node is a mappable dataset. Only applicable to leaf nodes
-  /// \return True if the dataset represented by this node is a mappable dataset
-  const bool IsMappable() const { return mappable_; }
+  /// \brief Check if this node is a mappable dataset. Only applicable to leaf nodes
+  /// \return True if this node is a mappable dataset
+  const bool IsMappable() const { return (mappable_ == kMappableSource); }
 
-  /// \brief  Check if this node is a descendant of an operator with cache. Currently used in leaf nodes
+  /// \brief Check if this node is a non-mappable dataset. Only applicable to leaf nodes
+  /// \return True if this node is a non-mappable dataset
+  const bool IsNonMappable() const { return (mappable_ == kNonMappableSource); }
+
+  /// \brief Check if this node is not a data source node.
+  /// \return True if this node is not a data source node
+  const bool IsNotADataSource() const { return (mappable_ == kNotADataSource); }
+
+  /// \brief Check if this node is a descendant of an operator with cache. Currently used in leaf nodes
   /// \return True if a cache-enabled operator is an ancestor of this node
   const bool IsDescendantOfCache() const { return descendant_of_cache_; }
 
-  /// \brief  Mark to indicate this node is a descendant of an operator with cache. Currently used in leaf nodes
+  /// \brief Mark to indicate this node is a descendant of an operator with cache. Currently used in leaf nodes
   void HasCacheAbove() { descendant_of_cache_ = true; }
 
+  /// \brief Getter of the number of workers
+  int32_t num_workers() { return num_workers_; }
+
   /// \brief Setter function for runtime number of workers
   /// \param[in] num_workers The number of threads in this operator
   /// \return Shared pointer to the original object
@@ -247,7 +261,7 @@ class DatasetNode : public std::enable_shared_from_this<DatasetNode> {
 
  protected:
   std::vector<std::shared_ptr<DatasetNode>> children_;
-  std::vector<DatasetNode *> parent_;
+  DatasetNode *parent_;  // used to record the only one parent of an IR node after parsing phase
   std::shared_ptr<DatasetCache> cache_;
   int64_t dataset_size_ = -1;
   int32_t num_workers_;
@@ -257,7 +271,8 @@ class DatasetNode : public std::enable_shared_from_this<DatasetNode> {
   std::string PrintColumns(const std::vector<std::string> &columns) const;
   Status AddCacheOp(std::vector<std::shared_ptr<DatasetOp>> *node_ops);
   void PrintNode(std::ostream &out, int *level) const;
-  bool mappable_;
+  enum DataSource { kNotADataSource = 0, kNonMappableSource = 1, kMappableSource = 2 };
+  enum DataSource mappable_;
   bool descendant_of_cache_;
 };
 
@@ -265,12 +280,12 @@ class DatasetNode : public std::enable_shared_from_this<DatasetNode> {
 class MappableSourceNode : public DatasetNode {
  public:
   /// \brief Constructor
-  MappableSourceNode() : DatasetNode() { mappable_ = true; }
+  MappableSourceNode() : DatasetNode() { mappable_ = kMappableSource; }
 
   /// \brief Constructor that initializes the cache
   /// \param dataset_cache DatasetCache
   explicit MappableSourceNode(const std::shared_ptr<DatasetCache> &dataset_cache) : DatasetNode(dataset_cache) {
-    mappable_ = true;
+    mappable_ = kMappableSource;
     // Initially set to false, and set to true by the optimizer when conditions are met.
     descendant_of_cache_ = false;
   }
@@ -287,12 +302,12 @@ class MappableSourceNode : public DatasetNode {
 class NonMappableSourceNode : public DatasetNode {
  public:
   /// \brief Constructor
-  NonMappableSourceNode() : DatasetNode() { mappable_ = false; }
+  NonMappableSourceNode() : DatasetNode() { mappable_ = kNonMappableSource; }
 
   /// \brief Constructor that initializes the cache
   /// \param dataset_cache DatasetCache
   explicit NonMappableSourceNode(const std::shared_ptr<DatasetCache> &dataset_cache) : DatasetNode(dataset_cache) {
-    mappable_ = false;
+    mappable_ = kNonMappableSource;
     // Initially set to false, and set to true by the optimizer when conditions are met.
     descendant_of_cache_ = false;
   }
diff --git a/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/root_node.cc b/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/root_node.cc
index 55ed794e10a..b0375e27914 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/root_node.cc
+++ b/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/root_node.cc
@@ -27,13 +27,14 @@ namespace mindspore {
 namespace dataset {
 
 // Constructor for RootNode
-RootNode::RootNode(std::shared_ptr<DatasetNode> child, int32_t num_epochs) : DatasetNode(), num_epochs_(num_epochs) {
-  // The root node's parent must remain nullptr. (which is set in the constructor of DatasetNode)
+RootNode::RootNode(std::shared_ptr<DatasetNode> child) : DatasetNode() {
+  // The root node's parent must remain nullptr, which is set in the constructor of DatasetNode.
   AddChild(child);
 }
 
 std::shared_ptr<DatasetNode> RootNode::Copy() {
-  auto node = std::make_shared<RootNode>(nullptr, num_epochs_);
+  auto node = std::make_shared<RootNode>(nullptr);
+  node->SetNumEpochs(num_epochs_);
   return node;
 }
 
@@ -54,7 +55,7 @@ Status RootNode::ValidateParams() {
     MS_LOG(ERROR) << err_msg;
     RETURN_STATUS_SYNTAX_ERROR(err_msg);
   }
-  if (parent_.size() != 0) {
+  if (parent_ != nullptr) {
     std::string err_msg = "Internal error: root node should not have a parent";
     MS_LOG(ERROR) << err_msg;
     RETURN_STATUS_SYNTAX_ERROR(err_msg);
diff --git a/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/root_node.h b/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/root_node.h
index 9dbdfecf820..a6a1ea2b598 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/root_node.h
+++ b/mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/root_node.h
@@ -29,7 +29,10 @@ namespace dataset {
 class RootNode : public DatasetNode {
  public:
   /// \brief Constructor
-  RootNode(std::shared_ptr<DatasetNode> child, int32_t num_epochs);
+  RootNode() : DatasetNode() {}
+
+  /// \brief Constructor
+  explicit RootNode(std::shared_ptr<DatasetNode> child);
 
   /// \brief Destructor
   ~RootNode() = default;
@@ -54,6 +57,9 @@ class RootNode : public DatasetNode {
   /// \brief Getter of number of epochs
   int32_t num_epochs() { return num_epochs_; }
 
+  /// \brief Setter of number of epochs
+  void SetNumEpochs(int32_t num_epochs) { num_epochs_ = num_epochs; }
+
   /// \brief Parameters validation
   /// \return Status Status::OK() if all the parameters are valid
   Status ValidateParams() override;
diff --git a/mindspore/ccsrc/minddata/dataset/engine/opt/CMakeLists.txt b/mindspore/ccsrc/minddata/dataset/engine/opt/CMakeLists.txt
index 44847ade49b..303e985ce41 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/opt/CMakeLists.txt
+++ b/mindspore/ccsrc/minddata/dataset/engine/opt/CMakeLists.txt
@@ -7,6 +7,7 @@ add_library(engine-opt OBJECT
           pre/cache_error_pass.cc
           pre/cache_transform_pass.cc
           pre/cache_validation_pass.cc
+          pre/deep_copy_pass.cc
           pre/epoch_ctrl_pass.cc
           pre/epoch_injection_pass.cc
           pre/getter_pass.cc
diff --git a/mindspore/ccsrc/minddata/dataset/engine/opt/pre/deep_copy_pass.cc b/mindspore/ccsrc/minddata/dataset/engine/opt/pre/deep_copy_pass.cc
new file mode 100644
index 00000000000..cd20df18dbe
--- /dev/null
+++ b/mindspore/ccsrc/minddata/dataset/engine/opt/pre/deep_copy_pass.cc
@@ -0,0 +1,69 @@
+/**
+ * Copyright 2020 Huawei Technologies Co., Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <string>
+#include "minddata/dataset/include/datasets.h"
+#include "minddata/dataset/engine/opt/pre/deep_copy_pass.h"
+#include "minddata/dataset/engine/ir/datasetops/root_node.h"
+
+namespace mindspore {
+namespace dataset {
+
+DeepCopyPass::DeepCopyPass() {
+  root_ = std::make_shared<RootNode>();
+  parent_ = root_.get();
+}
+
+Status DeepCopyPass::Visit(std::shared_ptr<DatasetNode> node, bool *modified) {
+  *modified = true;
+  // Do a nested-loop walk to check whether a node has the same child more than once.
+  // This is an artificial restriction. We can support it since we will do a clone of the input tree in this pass.
+  // Example:  ds2 = ds1 + ds1;
+  auto children = node->Children();
+  if (children.size() > 0) {
+    for (auto it1 = children.begin(); it1 != children.end() - 1; ++it1) {
+      for (auto it2 = it1 + 1; it2 != children.end(); ++it2) {
+        if (*it1 == *it2) {
+          std::string err_msg = "The same node " + (*it1)->Name() + " is a child of its parent more than once.";
+          RETURN_STATUS_UNEXPECTED(err_msg);
+        }
+      }
+    }
+  }
+
+  // Clone a new copy of this node
+  std::shared_ptr<DatasetNode> new_node = node->Copy();
+  // Temporary fix to set the num_workers to each cloned node.
+  // This can be improved by adding a new method in the base class DatasetNode to transfer the properties to
+  // the cloned node. Each derived class's Copy() will need to include this method.
+  new_node->SetNumWorkers(node->num_workers());
+  // This method below assumes a DFS walk and from the first child to the last child.
+  // Future: A more robust implementation that does not depend on the above assumption.
+  parent_->AppendChild(new_node);
+
+  // Then set this node to be a new parent to accept a copy of its next child
+  parent_ = new_node.get();
+  return Status::OK();
+}
+
+Status DeepCopyPass::VisitAfter(std::shared_ptr<DatasetNode> node, bool *modified) {
+  *modified = true;
+  // After visit the node, move up to its parent
+  parent_ = parent_->Parent();
+  return Status::OK();
+}
+}  // namespace dataset
+}  // namespace mindspore
diff --git a/mindspore/ccsrc/minddata/dataset/engine/opt/pre/deep_copy_pass.h b/mindspore/ccsrc/minddata/dataset/engine/opt/pre/deep_copy_pass.h
new file mode 100644
index 00000000000..76daa72a71a
--- /dev/null
+++ b/mindspore/ccsrc/minddata/dataset/engine/opt/pre/deep_copy_pass.h
@@ -0,0 +1,61 @@
+/**
+ * Copyright 2020 Huawei Technologies Co., Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef DATASET_ENGINE_OPT_PRE_DEEP_COPY_PASS_H_
+#define DATASET_ENGINE_OPT_PRE_DEEP_COPY_PASS_H_
+
+#include <memory>
+#include <vector>
+#include "minddata/dataset/engine/opt/pass.h"
+
+namespace mindspore {
+namespace dataset {
+
+/// \class DeepCopyPass
+/// \brief This pass clones a new copy of IR tree. A new copy is used in the compilation to avoid any modification to
+///    the IR tree associated with the user code.
+class DeepCopyPass : public IRNodePass {
+ public:
+  /// \brief Constructor
+  DeepCopyPass();
+
+  /// \brief Destructor
+  ~DeepCopyPass() = default;
+
+  /// \brief Clone a new copy of the node
+  /// \param[in] node The node being visited
+  /// \param[inout] *modified indicates whether the node has been visited
+  /// \return Status code
+  Status Visit(std::shared_ptr<DatasetNode> node, bool *modified) override;
+
+  /// \brief Reset parent after walking its sub tree.
+  /// \param[in] node The node being visited
+  /// \param[inout] *modified indicates whether the node has been visited
+  /// \return Status code
+  Status VisitAfter(std::shared_ptr<DatasetNode> node, bool *modified) override;
+
+  /// \brief Getter method to retrieve the root node
+  /// \return the root node of the new cloned tree
+  std::shared_ptr<RootNode> Root() { return root_; }
+
+ private:
+  std::shared_ptr<RootNode> root_;
+  DatasetNode *parent_;
+};
+}  // namespace dataset
+}  // namespace mindspore
+
+#endif  // DATASET_ENGINE_OPT_PRE_DEEP_COPY_PASS_H_
diff --git a/mindspore/ccsrc/minddata/dataset/engine/opt/pre/input_validation_pass.cc b/mindspore/ccsrc/minddata/dataset/engine/opt/pre/input_validation_pass.cc
index 8fff7473b03..5ede8c12d60 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/opt/pre/input_validation_pass.cc
+++ b/mindspore/ccsrc/minddata/dataset/engine/opt/pre/input_validation_pass.cc
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <string>
 #include <vector>
 #include "minddata/dataset/include/datasets.h"
 #include "minddata/dataset/engine/opt/pre/input_validation_pass.h"
@@ -24,6 +25,19 @@ namespace dataset {
 Status InputValidationPass::Visit(std::shared_ptr<DatasetNode> node, bool *modified) {
   *modified = false;
   RETURN_IF_NOT_OK(node->ValidateParams());
+
+  // A data source node must be a leaf node
+  if ((node->IsMappable() || node->IsNonMappable()) && !node->IsLeaf()) {
+    std::string err_msg = node->Name() + " is a data source and must be a leaf node.";
+    RETURN_STATUS_UNEXPECTED(err_msg);
+  }
+
+  // A non-leaf node must not be a data source node
+  if (node->IsNotADataSource() && node->IsLeaf()) {
+    std::string err_msg = node->Name() + " is a dataset operator and must not be a leaf node.";
+    RETURN_STATUS_UNEXPECTED(err_msg);
+  }
+
   return Status::OK();
 }
 }  // namespace dataset
diff --git a/mindspore/ccsrc/minddata/dataset/engine/tree_adapter.cc b/mindspore/ccsrc/minddata/dataset/engine/tree_adapter.cc
index c74e750959a..b7cb9ce0b4b 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/tree_adapter.cc
+++ b/mindspore/ccsrc/minddata/dataset/engine/tree_adapter.cc
@@ -20,6 +20,7 @@
 #include "minddata/dataset/engine/ir/datasetops/root_node.h"
 #include "minddata/dataset/engine/opt/pass.h"
 #include "minddata/dataset/engine/opt/pre/cache_validation_pass.h"
+#include "minddata/dataset/engine/opt/pre/deep_copy_pass.h"
 #include "minddata/dataset/engine/opt/pre/epoch_ctrl_pass.h"
 #include "minddata/dataset/engine/opt/pre/input_validation_pass.h"
 #include "minddata/dataset/engine/opt/pre/node_removal_pass.h"
@@ -27,6 +28,11 @@
 namespace mindspore {
 namespace dataset {
 
+TreeAdapter::TreeAdapter() {
+  tree_state_ = kCompileStateInit;
+  optimize_ = common::GetEnv("OPTIMIZE") == "true" ? true : false;
+}
+
 Status TreeAdapter::PrePass(std::shared_ptr<DatasetNode> ir) {
   // Vector of actions in pre-pass phase
   std::vector<std::unique_ptr<IRPass>> actions;
@@ -86,7 +92,7 @@ Status TreeAdapter::PostPass(std::shared_ptr<DatasetNode> ir) {
   return Status::OK();
 }
 
-Status TreeAdapter::BuildExecutionTree(std::shared_ptr<DatasetNode> ir, std::shared_ptr<DatasetOp> *op) {
+Status TreeAdapter::BuildExecutionTreeRecur(std::shared_ptr<DatasetNode> ir, std::shared_ptr<DatasetOp> *op) {
   // Build the DatasetOp ExecutionTree from the optimized IR tree
   std::vector<std::shared_ptr<DatasetOp>> ops;
   RETURN_IF_NOT_OK(ir->Build(&ops));
@@ -104,47 +110,20 @@ Status TreeAdapter::BuildExecutionTree(std::shared_ptr<DatasetNode> ir, std::sha
   // Build the children of IR, once they return, add the return value to *op
   for (std::shared_ptr<DatasetNode> child_ir : ir->Children()) {
     std::shared_ptr<DatasetOp> child_op;
-    RETURN_IF_NOT_OK(BuildExecutionTree(child_ir, &child_op));
+    RETURN_IF_NOT_OK(BuildExecutionTreeRecur(child_ir, &child_op));
     RETURN_IF_NOT_OK(ops.back()->AddChild(child_op));  // append children to the last of ops
   }
 
   return Status::OK();
 }
 
-Status TreeAdapter::Compile(std::shared_ptr<DatasetNode> input_ir, int32_t num_epochs) {
-  optimize_ = true;  // Always ON (temporary)
-
-  RETURN_UNEXPECTED_IF_NULL(input_ir);
-  MS_LOG(INFO) << "Input plan:" << '\n' << *input_ir << '\n';
-
-  // We will first walk the input tree to sanity check this is not a graph
-  // Flag an error when it is not a tree
-  CHECK_FAIL_RETURN_UNEXPECTED(input_ir->IsTree(), "The data pipeline is not a tree (i.e. one node has two consumers)");
-
-  // Copy the input IR tree and insert under the root node
-  // Create a root node to host the new copy of the input IR tree to pass to the optimizer
-  auto root_ir = std::make_shared<RootNode>(input_ir->DeepCopy(), num_epochs);
-  MS_LOG(INFO) << "Plan before PrePass:" << '\n' << *root_ir << '\n';
-
-  // Pre-pass of the IR tree
-  RETURN_IF_NOT_OK(PrePass(root_ir));
-
-  // Optional phase of optimization
-  if (optimize_) {
-    RETURN_IF_NOT_OK(Optimize(root_ir));
-  }
-
-  // Post-pass of the IR tree
-  RETURN_IF_NOT_OK(PostPass(root_ir));
-
-  MS_LOG(INFO) << "Plan after PostPass:" << '\n' << *root_ir << '\n';
-
+Status TreeAdapter::Build(std::shared_ptr<DatasetNode> root_ir, int32_t num_epochs) {
   // This will evolve in the long run
   tree_ = std::make_unique<ExecutionTree>();
 
   // Build the Execution tree from the child of the IR root node, which represent the root of the input IR tree
   std::shared_ptr<DatasetOp> root_op;
-  RETURN_IF_NOT_OK(BuildExecutionTree(root_ir->Children()[0], &root_op));
+  RETURN_IF_NOT_OK(BuildExecutionTreeRecur(root_ir->Children()[0], &root_op));
   RETURN_IF_NOT_OK(tree_->AssignRoot(root_op));
 
   if (pre_pass_override_) tree_->SetPrePassOverride(pre_pass_override_);
@@ -165,6 +144,48 @@ Status TreeAdapter::Compile(std::shared_ptr<DatasetNode> input_ir, int32_t num_e
   return Status::OK();
 }
 
+Status TreeAdapter::Compile(std::shared_ptr<DatasetNode> input_ir, int32_t num_epochs) {
+  RETURN_UNEXPECTED_IF_NULL(input_ir);
+
+  tree_state_ = kCompileStateIRGraphBuilt;
+  MS_LOG(INFO) << "Input plan:" << '\n' << *input_ir << '\n';
+
+  // Clone the input IR tree and insert under the root node
+  // Create a root node to host the new copy of the input IR tree
+  // This is done so that the compilation will process and modify the tree
+  // without changing the tree associated with the user code.
+  // The tree from the user code is permitted to form a graph where any node
+  // is consumed by more than one parent. However, this cloning process here
+  // will break the graph into a tree by copying each consumption of a node into a new copy.
+  bool m = false;
+  DeepCopyPass cloning_tree;
+  RETURN_IF_NOT_OK(cloning_tree.Run(input_ir, &m));
+  std::shared_ptr<RootNode> root_ir = cloning_tree.Root();
+  root_ir->SetNumEpochs(num_epochs);
+
+  tree_state_ = kCompileStateIRTreeCloned;
+  MS_LOG(INFO) << "Plan before optimization:" << '\n' << *root_ir << '\n';
+
+  // Pre-pass of the IR tree
+  RETURN_IF_NOT_OK(PrePass(root_ir));
+
+  // Optional phase of optimization
+  if (optimize_) {
+    RETURN_IF_NOT_OK(Optimize(root_ir));
+  }
+
+  // Post-pass of the IR tree
+  RETURN_IF_NOT_OK(PostPass(root_ir));
+
+  tree_state_ = kCompileStateOptimized;
+  MS_LOG(INFO) << "Plan after optimization:" << '\n' << *root_ir << '\n';
+
+  RETURN_IF_NOT_OK(Build(root_ir, num_epochs));
+  tree_state_ = kCompileStateReady;
+
+  return Status::OK();
+}
+
 Status TreeAdapter::GetNext(TensorRow *row) {
   RETURN_UNEXPECTED_IF_NULL(tree_);
   RETURN_UNEXPECTED_IF_NULL(row);
diff --git a/mindspore/ccsrc/minddata/dataset/engine/tree_adapter.h b/mindspore/ccsrc/minddata/dataset/engine/tree_adapter.h
index 6e95ae0a60c..84a08cbc400 100644
--- a/mindspore/ccsrc/minddata/dataset/engine/tree_adapter.h
+++ b/mindspore/ccsrc/minddata/dataset/engine/tree_adapter.h
@@ -33,7 +33,7 @@ class DatasetNode;
 
 class TreeAdapter {
  public:
-  TreeAdapter() = default;
+  TreeAdapter();
 
   ~TreeAdapter() = default;
 
@@ -68,28 +68,40 @@ class TreeAdapter {
   bool OptimizationEnabled() const { return optimize_; }
 
  private:
-  // This function runs a mandatory pass checking the syntax and semantics of the IR tree.
+  // Run the mandatory pass checking the syntax and semantics of the IR tree
   Status PrePass(std::shared_ptr<DatasetNode> ir);
 
-  // This function runs an optional optimization pass on the IR tree.
+  // Run the optional optimization pass on the IR tree
   Status Optimize(std::shared_ptr<DatasetNode> ir);
 
-  // This function runs a mandatory pass augmenting the IR tree before the execution.
+  // Run the mandatory pass augmenting the IR tree
   Status PostPass(std::shared_ptr<DatasetNode> ir);
 
+  // Build an Execution tree
+  Status Build(std::shared_ptr<DatasetNode> root_ir, int32_t num_epochs);
+
   // This RECURSIVE function walks the (optimized) IR tree in DFS to build its corresponding Execution tree.
-  Status BuildExecutionTree(std::shared_ptr<DatasetNode> ir, std::shared_ptr<DatasetOp> *op);
+  Status BuildExecutionTreeRecur(std::shared_ptr<DatasetNode> ir, std::shared_ptr<DatasetOp> *op);
 
   std::unique_ptr<DataBuffer> cur_db_;
   std::unordered_map<std::string, int32_t> column_name_map_;
-  std::unique_ptr<ExecutionTree> tree_;  // current connector capacity of root op, used for profiling
-  int32_t num_epochs_;
+  std::unique_ptr<ExecutionTree> tree_;                // current connector capacity of root op, used for profiling
   bool optimize_;                                      // Flag to enable optional optimization pass
   std::shared_ptr<DatasetIteratorTracing> tracing_;    // trace profiling data
   int32_t cur_batch_num_;                              // current batch number, used for profiling
   int32_t cur_connector_size_;                         // current connector size of root op, used for profiling
   int32_t cur_connector_capacity_;                     // current connector capacity of root op, used for profiling
   std::function<OptPass(OptPass)> pre_pass_override_;  // function ptr that overrides pre pass, called in PrePrepare()
+
+  // State flags for the lifecycle of the tree
+  enum CompileState {
+    kCompileStateInit = 0,      // The freshly initialized state
+    kCompileStateIRGraphBuilt,  // User code has been parsed and its IR graph built
+    kCompileStateIRTreeCloned,  // IR tree has been cloned from the IR graph
+    kCompileStateOptimized,     // IR tree has been optimized
+    kCompileStateReady          // Execution tree is generated from the optimized IR
+  };
+  CompileState tree_state_;
 };
 }  // namespace dataset
 }  // namespace mindspore
diff --git a/tests/ut/cpp/dataset/CMakeLists.txt b/tests/ut/cpp/dataset/CMakeLists.txt
index 498959fc3f4..a14b68b5ae4 100644
--- a/tests/ut/cpp/dataset/CMakeLists.txt
+++ b/tests/ut/cpp/dataset/CMakeLists.txt
@@ -65,7 +65,6 @@ SET(DE_UT_SRCS
         image_folder_op_test.cc
         image_process_test.cc
         interrupt_test.cc
-        ir_node_test.cc
         jieba_tokenizer_op_test.cc
         main_test.cc
         map_op_test.cc
diff --git a/tests/ut/cpp/dataset/ir_node_test.cc b/tests/ut/cpp/dataset/ir_node_test.cc
deleted file mode 100644
index 513de18a330..00000000000
--- a/tests/ut/cpp/dataset/ir_node_test.cc
+++ /dev/null
@@ -1,137 +0,0 @@
-/**
- * Copyright 2020 Huawei Technologies Co., Ltd
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#include <memory>
-#include <string>
-#include "common/common.h"
-#include "gtest/gtest.h"
-
-#include "minddata/dataset/engine/ir/datasetops/dataset_node.h"
-#include "minddata/dataset/engine/opt/pre/getter_pass.h"
-
-using namespace mindspore::dataset;
-
-class MindDataTestIRNodes : public UT::DatasetOpTesting {
- public:
-  MindDataTestIRNodes() = default;
-  // compare the ptr of the nodes in two trees, used to test the deep copy of nodes, will return error code
-  // if (ptr1 == ptr2) does not equal to flag or the two tree has different structures (or node names are not the same)
-  Status CompareTwoTrees(std::shared_ptr<DatasetNode> root1, std::shared_ptr<DatasetNode> root2, bool flag) {
-    CHECK_FAIL_RETURN_UNEXPECTED(root1 != nullptr && root2 != nullptr, "Error in Compare, nullptr.");
-    if (((root1.get() == root2.get()) != flag) || (root1->Name() != root2->Name())) {
-      std::string err_msg =
-        "Expect node ptr " + root1->Name() + (flag ? "==" : "!=") + root2->Name() + " but they aren't!";
-      RETURN_STATUS_UNEXPECTED(err_msg);
-    }
-
-    size_t num_child = root1->Children().size();
-
-    CHECK_FAIL_RETURN_UNEXPECTED(num_child == root2->Children().size(),
-                                 root1->Name() + " has " + std::to_string(num_child) + "child, node #2 has " +
-                                   std::to_string(root2->Children().size()) + " child.");
-
-    for (size_t ind = 0; ind < num_child; ind++) {
-      RETURN_IF_NOT_OK(CompareTwoTrees(root1->Children()[ind], root2->Children()[ind], flag));
-    }
-    return Status::OK();
-  }
-
-  // print the node's name in post order
-  Status PostOrderPrintTree(std::shared_ptr<DatasetNode> ir, std::string &names) {
-    RETURN_UNEXPECTED_IF_NULL(ir);
-    for (auto child : ir->Children()) {
-      RETURN_IF_NOT_OK(PostOrderPrintTree(child, names));
-    }
-    names += (ir->Name() + "->");
-    return Status::OK();
-  }
-};
-
-TEST_F(MindDataTestIRNodes, MindDataTestSimpleDeepCopy) {
-  MS_LOG(INFO) << "Doing MindDataTestIRNodes-MindDataTestSimpleDeepCopy.";
-
-  auto tree1 = RandomData(44)->Repeat(2)->Project({"label"})->Shuffle(10)->Batch(2)->IRNode();
-
-  auto tree2 = tree1->DeepCopy();
-  std::string tree_1_names, tree_2_names;
-
-  ASSERT_OK(PostOrderPrintTree(tree1, tree_1_names));
-  ASSERT_OK(PostOrderPrintTree(tree2, tree_2_names));
-
-  // expected output for the 2 names:
-  // RandomDataset->Repeat->Project->Shuffle->Batch->
-  EXPECT_EQ(tree_1_names, tree_2_names);
-
-  ASSERT_OK(CompareTwoTrees(tree1, tree1, true));
-  ASSERT_OK(CompareTwoTrees(tree1, tree2, false));
-
-  // verify compare function is correct
-  EXPECT_TRUE(CompareTwoTrees(tree2, tree2, false).IsError());
-}
-
-TEST_F(MindDataTestIRNodes, MindDataTestZipDeepCopy) {
-  MS_LOG(INFO) << "Doing MindDataTestIRNodes-MindDataTestZipDeepCopy.";
-
-  auto branch1 = RandomData(44)->Project({"label"});
-  auto branch2 = RandomData(44)->Shuffle(10);
-
-  auto tree1 = Zip({branch1, branch2})->Batch(2)->IRNode();
-
-  auto tree2 = tree1->DeepCopy();
-  std::string tree_1_names, tree_2_names;
-
-  ASSERT_OK(PostOrderPrintTree(tree1, tree_1_names));
-  ASSERT_OK(PostOrderPrintTree(tree2, tree_2_names));
-
-  // expected output for the 2 names:
-  // RandomDataset->Project->RandomDataset->Shuffle->Zip->Batch->
-  EXPECT_EQ(tree_1_names, tree_2_names);
-
-  // verify the pointer within the same tree are the same
-  ASSERT_OK(CompareTwoTrees(tree1, tree1, true));
-  // verify two trees
-  ASSERT_OK(CompareTwoTrees(tree1, tree2, false));
-}
-
-TEST_F(MindDataTestIRNodes, MindDataTestNodeRemove) {
-  MS_LOG(INFO) << "Doing MindDataTestIRNodes-MindDataTestNodeRemove.";
-
-  auto branch1 = RandomData(44)->Project({"label"});
-  auto branch2 = ImageFolder("path");
-  auto tree = Zip({branch1, branch2})->IRNode();
-  /***
-   tree looks like this, we will remove node and test its functionalities
-            Zip
-           /   \
-      Project  ImageFolder
-        /
-    RandomData
-  ***/
-  auto tree_copy_1 = tree->DeepCopy();
-  ASSERT_EQ(tree_copy_1->Children().size(), 2);
-  // remove the project in the tree and test
-  ASSERT_OK(tree_copy_1->Children()[0]->Remove());  // remove Project from tree
-  ASSERT_OK(CompareTwoTrees(tree_copy_1, Zip({RandomData(44), ImageFolder("path")})->IRNode(), false));
-  // remove the ImageFolder, a leaf node from the tree
-  std::string tree_1_names, tree_2_names;
-  ASSERT_OK(PostOrderPrintTree(tree_copy_1, tree_1_names));
-  EXPECT_EQ(tree_1_names, "RandomDataset->ImageFolderDataset->Zip->");
-  auto tree_copy_2 = tree->DeepCopy();
-  ASSERT_EQ(tree_copy_2->Children().size(), 2);
-  tree_copy_2->Children()[1]->Remove();
-  ASSERT_OK(PostOrderPrintTree(tree_copy_2, tree_2_names));
-  EXPECT_EQ(tree_2_names, "RandomDataset->Project->Zip->");
-}