| # | Problem | Level |
|---|---|---|
| 94 | Binary Tree Inorder Traversal | Medium |
| 95 | Unique Binary Search Trees -II | Medium |
| 449 | Serialize & Deserialize a BST | Medium |
| 450 | Delete a Node in a BST | Medium |
| 501 | Find Mode in Binary Search Tree | Medium |
| 508 | Most Frequent Subtree sum | Medium |