def METHOD_NAME(self):
    # init list of trees
    self.world_volumes_user_info = (
        self.simulation_engine.simulation.volume_manager.separate_parallel_worlds()
    )
    # build G4 parallel volume engine (except for main world)
    for world_name in self.world_volumes_user_info:
        if (
            world_name
            == self.simulation_engine.simulation.volume_manager.world_name
        ):
            continue
        # register a new parallel world
        volumes_user_info = self.world_volumes_user_info[world_name]
        pw = gate.ParallelVolumeEngine(self, world_name, volumes_user_info)
        self.RegisterParallelWorld(pw)
        # store it to avoid destruction
        self.parallel_volume_engines.append(pw)