Add tree problems

Author: ashishps1

README.md

@@ -58,6 +58,32 @@ This repository contains LeetCode resources which are useful during interview pr
 - [Coursera - Algorithms, Part 2](https://www.coursera.org/learn/algorithms-part2)
 
 ## Must-Do Problems (Topic Wise)
+### Trees
+  - [Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/description/)
+  - [Convert Sorted Array to Binary Search Tree](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/)
+  - [Count Complete Tree Nodes](https://leetcode.com/problems/count-complete-tree-nodes/description/)
+  - [All Possible Full Binary Trees](https://leetcode.com/problems/all-possible-full-binary-trees/description/)
+  - [Delete Leaves With a Given Value](https://leetcode.com/problems/delete-leaves-with-a-given-value/description/)
+  - [Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/description/)
+  - [Longest Univalue Path](https://leetcode.com/problems/longest-univalue-path/description/)
+  - [Delete Nodes And Return Forest](https://leetcode.com/problems/delete-nodes-and-return-forest/description/)
+  - [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/description/)
+  - [Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/description/)
+  - [All Nodes Distance K in Binary Tree](https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree/description/)
+  - [Maximum Difference Between Node and Ancestor](https://leetcode.com/problems/maximum-difference-between-node-and-ancestor/description/)
+  - [Find Duplicate Subtrees](https://leetcode.com/problems/find-duplicate-subtrees/description/)
+  - [Flatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/description/)
+  - [House Robber III](https://leetcode.com/problems/house-robber-iii/description/)
+  - [Step-By-Step Directions From a Binary Tree Node to Another](https://leetcode.com/problems/step-by-step-directions-from-a-binary-tree-node-to-another/description/)
+  - [Delete Node in a BST](https://leetcode.com/problems/delete-node-in-a-bst/description/)
+  - [Populating Next Right Pointers in Each Node II](https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/description/)
+  - [Trim a Binary Search Tree](https://leetcode.com/problems/trim-a-binary-search-tree/description/)
+  - [Distribute Coins in Binary Tree](https://leetcode.com/problems/distribute-coins-in-binary-tree/description/)
+  - [Binary Search Tree to Greater Sum Tree](https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/description/)
+  - [Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/description/)
+  - [Binary Tree Cameras](https://leetcode.com/problems/binary-tree-cameras/description/)
+  - [Binary Tree Maximum Path Sum](https://leetcode.com/problems/binary-tree-maximum-path-sum/description/)
+  - [Maximum Sum BST in Binary Tree](https://leetcode.com/problems/maximum-sum-bst-in-binary-tree/description/)
 ### Tries
   - [Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree/description/)
   - [Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/description/)