Configure the filter.
        
        @type  graph: graph
        @param graph: Graph.
        
        @type  spanning_tree: dictionary
        @param spanning_tree: Spanning tree.

def configure(self, graph, spanning_tree):
        """
        Configure the filter.
        
        @type  graph: graph
        @param graph: Graph.
        
        @type  spanning_tree: dictionary
        @param spanning_tree: Spanning tree.
        """
        self.graph = graph
        self.spanning_tree = spanning_tree