Android : Stacking Notifications does not work

I need to form a group of notifications. I made the example enter link description here

but my notice are not grouped. what did I do wrong?

my code:

private static int id =0;
    final static String GROUP_KEY_GUEST = "group_key_guest";


     private static void generateNotification(Context context, String message) {

            NotificationManagerCompat notificationManager = NotificationManagerCompat.from(context);

            Intent intent = new Intent(context,MyActivity.class);
            PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, PendingIntent.FLAG_CANCEL_CURRENT);

            Notification notification   = new NotificationCompat.Builder(context)
                    .setContentIntent(pendingIntent)
                    .setSmallIcon(R.drawable.ic_stat_gcm)
                    .setLargeIcon(BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_stat_gcm))
                    .setTicker("New Message")
                    .setWhen(System.currentTimeMillis())
                    .setAutoCancel(true)
                    .setContentTitle("Message")
                    .setContentText(message)
                    .setGroup(GROUP_KEY_GUEST)
                    .build();

            notificationManager.notify(id++, notification);
        }

method call:

 @Override
    protected void onMessage(Context context, Intent intent) {
        Log.d(TAG, "Поступило сообщение: " + intent.getExtras());
        String message = intent.getStringExtra("content");
        generateNotification(context, message);
    }