Insert new key into node

def insert(self, key):
        """
        Insert new key into node
        """
        # Create new node
        n = TreeNode(key)
        if not self.node:
            self.node = n
            self.node.left = AvlTree()
            self.node.right = AvlTree()
        elif key < self.node.val:
            self.node.left.insert(key)
        elif key > self.node.val:
            self.node.right.insert(key)
        self.re_balance()