Update 17-trees.md

Author: kunal-kushwaha

assignments/17-trees.md

@@ -22,6 +22,7 @@
 ## Medium
 
 - [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/) `leetcode`
+- [All Nodes Distance K in Binary Tree](https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree/) `leetcode`
 - [Validate Binary Tree Nodes](https://leetcode.com/problems/validate-binary-tree-nodes/) `leetcode`
 - [Longest Univalue Path](https://leetcode.com/problems/longest-univalue-path/) `leetcode`
 - [Closest Nodes Queries in a Binary Search Tree](https://leetcode.com/problems/closest-nodes-queries-in-a-binary-search-tree/) `leetcode`