<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _ancestors(self):
 """Attribute referencing the tree ancestors of the node instance. :returns: list of node ancestors in sequence, first item is the current node instance (`self`), the last item is root. :rtype: list of Node references """

        # return list of ancestor nodes starting with self.parent and ending with root
        _ancestors=[]
        _n = self
        while _n.parent:
            _n = _n.parent
            _ancestors.append(_n)
        return _ancestors