输入一棵二叉树，求该树的深度。从根结点到叶结点依次经过的结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。

/** public class TreeNode { int val = 0; TreeNode left = null; TreeNode right = null; public TreeNode(int val) { this.val = val; } } */
public class Solution {
   
    public int TreeDepth(TreeNode root) {
   
        if(root==null)
            return 0;
        int leftNum=TreeDepth(root.left);
        int rightNum=TreeDepth(root.right);
         
        return leftNum>rightNum?(leftNum+1):(rightNum+1);
    }
}