leetcode 701

此题是水题，只需要进行查找，找到对应的位置，然后把数字插进去即可。

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def insertIntoBST(self, root, val):
        """
        :type root: TreeNode
        :type val: int
        :rtype: TreeNode
        """
        
        if root == None:
            return TreeNode(val)
        
        if root.val > val:
            root.left = self.insertIntoBST(root.left,val)
        else:
            root.right = self.insertIntoBST(root.right,val)
        return root