def __init__(root_object, id_attr='', children_attr='', request=None,
    request_variable='', expanded_nodes=[], set_cookie=1):
    """
        'root_object' is the root object of the tree.

        'id_attr' and 'children_attr': see docstring for
        Node.__init__().

        'request' is the HTTP request.

        'request_variable' is the name of a request variable that
        contains the tree expansion information.
        """
