def upsideDownBinaryTree(self, root):
    if root is None or root.left is None:
        return root

    parent = None
    curr_node = root
    new_node = None
    last_right = None

    while curr_node is not None:
        new_node = curr_node.left
        curr_node.left = last_right
        last_right = curr_node.right
        curr_node.right = parent
        parent = curr_node
        curr_node = new_node
    return parent