Returns all nodes that share the same parent (incoming node) with
        the given node, including the node itself.

def siblings(self, node):
        """Returns all nodes that share the same parent (incoming node) with
        the given node, including the node itself.
        """
        incoming = self.incoming(node)
        # TODO: Not handling the case of multiple incoming nodes yet
        if len(incoming) == 1:
            incoming = incoming[0]
            siblings = self.outgoing(incoming)
            return siblings
        else:
            return [node]