Given a binary tree, find its height.

The height of a tree is defined as the number of edges on the longest path from the root to a leaf node. A leaf node is a node that does not have any children.

Examples:

Input: root[] = [12, 8, 18, 5, 11] 
 
Output: 2
Explanation: One of the longest path from the root (node 12) goes through node 8 to node 5, which has 2 edges.

Input: root[] = [1, 2, 3, 4, N, N, 5, N, N, 6, 7]  

Output: 3
Explanation: The longest path from the root (node 1) to a leaf node 6 with 3 edge.

Constraints:
1 <= number of nodes <= 10⁵
0 <= node->data <= 10⁵