def path_from_node_to_root(root, letter):
    """Recursive formula to reach a node
     Args:
         root: root node
         letter: letter to find
     Returns:
         list: list of the path
    """
    if root is None:
        return None

    elif root.get_letter() == letter:
        return []

    left_answer = path_from_node_to_root(root.left, letter)
    if left_answer is not None:
        left_answer.append(0)
        return left_answer

    right_answer = path_from_node_to_root(root.right, letter)
    if right_answer is not None:
        right_answer.append(1)
        return right_answer
    return None