Android multiple line notification like Gmail app

I am trying to create a multiple line notification like the Gmail application does as shown in the image below (the 5 notifications grouped under one notification)

I have tried various examples but can only seem to create single notifications like

   public void createSingleNotification(String title, String messageText, String tickerttext) {
        int icon = R.drawable.notification_icon; // icon from resources
        CharSequence tickerText = tickerttext; // ticker-text
        long when = System.currentTimeMillis(); // notification time
        Context context = getApplicationContext(); // application Context
        CharSequence contentTitle = title; // expanded message title
        CharSequence contentText = messageText; // expanded message text
        Intent notificationIntent = new Intent(this, MainActivity.class);

        Bundle xtra = new Bundle();
        xtra.putString("title", title);
        xtra.putString("message", messageText);

        notificationIntent.putExtras(xtra);
        PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
          notificationIntent, PendingIntent.FLAG_ONE_SHOT
            + PendingIntent.FLAG_UPDATE_CURRENT);
        String ns = Context.NOTIFICATION_SERVICE;

        NotificationManager mNotificationManager = (NotificationManager) getSystemService(ns);
        Notification notification = new Notification(icon, tickerText, when);
        notification.setLatestEventInfo(context, contentTitle, contentText,   contentIntent);
        notification.defaults |= Notification.DEFAULT_LIGHTS;
        notification.defaults |= Notification.DEFAULT_SOUND;
        notification.defaults |= Notification.FLAG_AUTO_CANCEL;
        notification.flags = Notification.DEFAULT_LIGHTS
          | Notification.FLAG_AUTO_CANCEL;
        final int HELLO_ID = 0;
        mNotificationManager.notify(HELLO_ID, notification);
      }

I am not sure how to create a notification group that I can add lines to.