def METHOD_NAME(self) -> None:
    """Print the all the items as a tree."""
    def recursive_print(tree: List, indent: int) -> None:
        """Inner print function. """
        tab =  '   ' * indent if indent > 0 else ''
        for node in tree:
            print(f'{tab} └ {node}')
            if node.children:
                recursive_print(node.children, indent + 1)
    print(self)
    recursive_print(self.data, 0)