Android : Stacking Notifications. not grouped notice

I use 5 types of notifications in my application. Here is my code as I do:

public class GCMIntentService extends GCMBaseIntentService {
    private static int id =0;
    NotificationManagerCompat notificationManager;

    public GCMIntentService() {
        super(SENDER_ID);
    }

    @Override
    protected void onMessage(Context context, Intent intent) {
        String title = intent.getStringExtra("title");
        String message = intent.getStringExtra("content");
        String group = intent.getStringExtra("group");
        generateNotification(context,title, message,group);
    }
                  ...
    private void generateNotification(Context context, String title, String message,String group) {
        if(notificationManager==null){
            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("Новое сообщение")
                .setWhen(System.currentTimeMillis())
                .setAutoCancel(true)
                .setContentTitle(title)
                .setContentText(message)
                .setGroup(group)
                .setGroupSummary(true)
                .build();

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

Notifications come but are not grouped. I want to notice that have one type of grouped. The notification must be updated and it just increase the post count. Give me how to do it. I searched in Google and there but not found a solution.