def in_order_traverse(self):
result = []<EOL>if not self.node:<EOL><INDENT>return result<EOL><DEDENT>result.extend(self.node.left.in_order_traverse())<EOL>result.append(self.node.key)<EOL>result.extend(self.node.right.in_order_traverse())<EOL>return result<EOL>
In-order traversal of the tree