def main() -> None:  # Main function for testing.
    tree = Node(1)
    tree.left = Node(2)
    tree.right = Node(3)
    tree.left.left = Node(4)
    tree.left.right = Node(5)
    tree.left.right.left = Node(6)
    tree.right.left = Node(7)
    tree.right.left.left = Node(8)
    tree.right.left.left.right = Node(9)

    print(is_full_binary_tree(tree))
    print(depth_of_tree(tree))
    print("Tree is: ")
    display(tree)