插入二叉搜索树

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

class Solution(object):
    def insertIntoBST(self, root, val):
        """
        :type root: TreeNode
        :type val: int
        :rtype: TreeNode
        """
        if not root:
            node = TreeNode(val)
            return node
        if val < root.val:
            if not root.left:
                node = TreeNode(val)
                root.left = node
            else:
                self.insertIntoBST(root.left, val)
        else:
            if not root.right:
                node = TreeNode(val)
                root.right = node
            else:
                self.insertIntoBST(root.right, val)
        return root