snippet

 @Override
    public void start(Stage primaryStage) {
        ComboBox<Menu> cb = new ComboBox <> ();
		cb.setMinWidth(250); cb.setMinHeight(20);
        cb.setOnAction( (e) -> System.out.println("blah") );

		Menu someMenu = new Menu ("Toyota");

			Menu sedan = new Menu ("Sedan");
				MenuItem camry = new MenuItem("Camry");
			sedan.getItems().add(camry);

			Menu SUV = new Menu ("SUV");
		someMenu.getItems().addAll(sedan, SUV);

		Menu someMenu2 = new Menu ("Nissan");

			Menu sedan2 = new Menu ("Sedan");
				MenuItem sentra = new MenuItem("Sentra");
			sedan2.getItems().add(sentra);

			Menu SUV2 = new Menu ("SUV");
		someMenu2.getItems().addAll(sedan2, SUV2);

		cb.getItems().addAll(someMenu, someMenu2);

        StackPane root = new StackPane();
        root.getChildren().add(cb);

		Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
    }