def add_edge(self, u, v):
        """
        self = EulerTourForest()
        self.add_node(1)
        self.add_node(2)
        u, v = 1, 2
        """
        # ubin = self.find_root(u)
        ru = self.find_root(u)
        rv = self.find_root(v)
        ru = self.reroot(ru, u)
        rv = self.reroot(rv, v)

        ubin.set_child(vbin)

        pass