以下函数可以正确完成二叉搜索树的插入，并保持二叉搜索树性质

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

def insertNode(root, x):
    if not root:
        return TreeNode(x)
    if x < root.val:
        root.right = insertNode(root.right, x)
    else:
        root.left = insertNode(root.left, x)
    return root