def load_model(self, filename, mass):
        model_np = self.loader.loadModel(filename)
        model_np.ls()

        def make_bullet(source_np):
            resulting_node_path = NodePath('Intermediary holding transform')
            resulting_node_path.setTransform(source_np.getTransform())
            source_node = source_np.node()
            if type(source_node) == GeomNode:
                body = BulletRigidBodyNode('BodyNode')
                shape = BulletConvexHullShape()
                for geom in source_node.getGeoms():
                    geom = geom.decompose()
                    shape.addGeom(geom)
                body.addShape(shape)
                body.setMass(mass)
                self.world.attachRigidBody(body)
                body_np = resulting_node_path.attachNewNode(body)
                geom_np = NodePath('MovedGeom')
                geom_np.attachNewNode(source_node)
                geom_np.reparentTo(body_np)
            else:
                for child in source_np.getChildren():
                    child_result = make_bullet(child)
                    child_result.reparentTo(resulting_node_path)
            return resulting_node_path

        return make_bullet(model_np)