diff --git a/include/treelite/tree.h b/include/treelite/tree.h
index e7f39315..50b21307 100644
--- a/include/treelite/tree.h
+++ b/include/treelite/tree.h
@@ -278,7 +278,11 @@ class Tree {
   // vector of nodes
   ContiguousArray<Node> nodes_;
   ContiguousArray<LeafOutputType> leaf_vector_;
-  ContiguousArray<std::size_t> leaf_vector_offset_;
+  // Map nid to the start and end index in leaf_vector_
+  // We could use std::pair, but it is not POD, so easier to use two vectors
+  // here
+  ContiguousArray<std::size_t> leaf_vector_begin_;
+  ContiguousArray<std::size_t> leaf_vector_end_;
   ContiguousArray<uint32_t> matching_categories_;
   ContiguousArray<std::size_t> matching_categories_offset_;
 
@@ -369,8 +373,8 @@ class Tree {
    * \param nid ID of node being queried
    */
   inline std::vector<LeafOutputType> LeafVector(int nid) const {
-    const std::size_t offset_begin = leaf_vector_offset_.at(nid);
-    const std::size_t offset_end = leaf_vector_offset_.at(nid + 1);
+    const std::size_t offset_begin = leaf_vector_begin_.at(nid);
+    const std::size_t offset_end = leaf_vector_end_.at(nid);
     if (offset_begin >= leaf_vector_.Size() || offset_end > leaf_vector_.Size()) {
       // Return empty vector, to indicate the lack of leaf vector
       return std::vector<LeafOutputType>();
@@ -385,7 +389,7 @@ class Tree {
    * \param nid ID of node being queried
    */
   inline bool HasLeafVector(int nid) const {
-    return leaf_vector_offset_.at(nid) != leaf_vector_offset_.at(nid + 1);
+    return leaf_vector_begin_.at(nid) != leaf_vector_end_.at(nid);
   }
   /*!
    * \brief get threshold of the node
diff --git a/include/treelite/tree_impl.h b/include/treelite/tree_impl.h
index 05e38fa1..041f51d4 100644
--- a/include/treelite/tree_impl.h
+++ b/include/treelite/tree_impl.h
@@ -485,7 +485,8 @@ Tree<ThresholdType, LeafOutputType>::Clone() const {
   tree.num_nodes = num_nodes;
   tree.nodes_ = nodes_.Clone();
   tree.leaf_vector_ = leaf_vector_.Clone();
-  tree.leaf_vector_offset_ = leaf_vector_offset_.Clone();
+  tree.leaf_vector_begin_ = leaf_vector_begin_.Clone();
+  tree.leaf_vector_end_ = leaf_vector_end_.Clone();
   tree.matching_categories_ = matching_categories_.Clone();
   tree.matching_categories_offset_ = matching_categories_offset_.Clone();
   return tree;
@@ -501,7 +502,7 @@ Tree<ThresholdType, LeafOutputType>::GetFormatStringForNode() {
   }
 }
 
-constexpr std::size_t kNumFramePerTree = 6;
+constexpr std::size_t kNumFramePerTree = 7;
 
 template <typename ThresholdType, typename LeafOutputType>
 template <typename ScalarHandler, typename PrimitiveArrayHandler, typename CompositeArrayHandler>
@@ -512,7 +513,8 @@ Tree<ThresholdType, LeafOutputType>::SerializeTemplate(
   scalar_handler(&num_nodes);
   composite_array_handler(&nodes_, GetFormatStringForNode());
   primitive_array_handler(&leaf_vector_);
-  primitive_array_handler(&leaf_vector_offset_);
+  primitive_array_handler(&leaf_vector_begin_);
+  primitive_array_handler(&leaf_vector_end_);
   primitive_array_handler(&matching_categories_);
   primitive_array_handler(&matching_categories_offset_);
 }
@@ -528,7 +530,8 @@ Tree<ThresholdType, LeafOutputType>::DeserializeTemplate(
     throw std::runtime_error("Could not load the correct number of nodes");
   }
   array_handler(&leaf_vector_);
-  array_handler(&leaf_vector_offset_);
+  array_handler(&leaf_vector_begin_);
+  array_handler(&leaf_vector_end_);
   array_handler(&matching_categories_);
   array_handler(&matching_categories_offset_);
 }
@@ -614,7 +617,8 @@ Tree<ThresholdType, LeafOutputType>::AllocNode() {
     throw std::runtime_error("Invariant violated: nodes_ contains incorrect number of nodes");
   }
   for (int nid = nd; nid < num_nodes; ++nid) {
-    leaf_vector_offset_.PushBack(leaf_vector_offset_.Back());
+    leaf_vector_begin_.PushBack(0);
+    leaf_vector_end_.PushBack(0);
     matching_categories_offset_.PushBack(matching_categories_offset_.Back());
     nodes_.Resize(nodes_.Size() + 1);
     nodes_.Back().Init();
@@ -627,7 +631,8 @@ inline void
 Tree<ThresholdType, LeafOutputType>::Init() {
   num_nodes = 1;
   leaf_vector_.Clear();
-  leaf_vector_offset_.Resize(2, 0);
+  leaf_vector_begin_.Resize(1, {});
+  leaf_vector_end_.Resize(1, {});
   matching_categories_.Clear();
   matching_categories_offset_.Resize(2, 0);
   nodes_.Resize(1);
@@ -737,24 +742,12 @@ template <typename ThresholdType, typename LeafOutputType>
 inline void
 Tree<ThresholdType, LeafOutputType>::SetLeafVector(
     int nid, const std::vector<LeafOutputType>& node_leaf_vector) {
-  const std::size_t end_oft = leaf_vector_offset_.Back();
-  const std::size_t new_end_oft = end_oft + node_leaf_vector.size();
-  if (end_oft != leaf_vector_.Size()) {
-    throw std::runtime_error("Invariant violated");
-  }
-  if (!std::all_of(&leaf_vector_offset_.at(nid + 1), leaf_vector_offset_.End(),
-                   [end_oft](std::size_t x) { return (x == end_oft); })) {
-    throw std::runtime_error("Invariant violated");
-  }
-  // Hopefully we won't have to move any element as we add leaf vector elements for node nid
+  std::size_t begin = leaf_vector_.Size();
+  std::size_t end = begin + node_leaf_vector.size();
   leaf_vector_.Extend(node_leaf_vector);
-  if (new_end_oft != leaf_vector_.Size()) {
-    throw std::runtime_error("Invariant violated");
-  }
-  std::for_each(&leaf_vector_offset_.at(nid + 1), leaf_vector_offset_.End(),
-                [new_end_oft](std::size_t& x) { x = new_end_oft; });
-
-  Node& node = nodes_.at(nid);
+  leaf_vector_begin_[nid] = begin;
+  leaf_vector_end_[nid] = end;
+  Node &node = nodes_.at(nid);
   node.cleft_ = -1;
   node.cright_ = -1;
   node.split_type_ = SplitFeatureType::kNone;
diff --git a/src/json_serializer.cc b/src/json_serializer.cc
index 92fcac21..55f19d29 100644
--- a/src/json_serializer.cc
+++ b/src/json_serializer.cc
@@ -116,8 +116,10 @@ void SerializeTreeToJSON(WriterType& writer, const Tree<ThresholdType, LeafOutpu
   writer.Int(tree.num_nodes);
   writer.Key("leaf_vector");
   WriteContiguousArray(writer, tree.leaf_vector_);
-  writer.Key("leaf_vector_offset");
-  WriteContiguousArray(writer, tree.leaf_vector_offset_);
+  writer.Key("leaf_vector_begin");
+  WriteContiguousArray(writer, tree.leaf_vector_begin_);
+  writer.Key("leaf_vector_end");
+  WriteContiguousArray(writer, tree.leaf_vector_end_);
   writer.Key("matching_categories");
   WriteContiguousArray(writer, tree.matching_categories_);
   writer.Key("matching_categories_offset");
@@ -131,10 +133,8 @@ void SerializeTreeToJSON(WriterType& writer, const Tree<ThresholdType, LeafOutpu
 
   writer.EndObject();
 
-  // Sanity check
+  // Basic checks
   TREELITE_CHECK_EQ(tree.nodes_.Size(), tree.num_nodes);
-  TREELITE_CHECK_EQ(tree.nodes_.Size() + 1, tree.leaf_vector_offset_.Size());
-  TREELITE_CHECK_EQ(tree.leaf_vector_offset_.Back(), tree.leaf_vector_.Size());
   TREELITE_CHECK_EQ(tree.nodes_.Size() + 1, tree.matching_categories_offset_.Size());
   TREELITE_CHECK_EQ(tree.matching_categories_offset_.Back(), tree.matching_categories_.Size());
 }