As we know we have notification bar to show all the notifications in that are, in Android M we can show multiple notifications but from android N we can group them easily with better UI experience.

A summary will also add whenever user wants to add more than one notifications.

public class MainActivity extends AppCompatActivity {

    private NotificationsFragment mNotificationsFragment;

    protected static final String NOTIFICATION_DELETE
            = "delete";

    private BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            if (mNotificationsFragment == null) {
                checkFragment();
            }
            mNotificationsFragment.updateNotifications();
        }
    };

    @Override
    public void onCreate(Bundle savedInstanceState, PersistableBundle persistentState) {
        super.onCreate(savedInstanceState, persistentState);
        checkFragment();
        mFragment.updateNotifications();
    }

    private void checkFragment() {
        mFragment = (NotificationsFragment) getSupportFragmentManager()
                .findFragmentById(R.id.notificaiton_content_fragment);
    }

    @Override
    protected void onResume() {
        super.onResume();
        registerReceiver(mBroadcastReceiver, new IntentFilter(NOTIFICATION_DELETE));
    }

    @Override
    protected void onPause() {
        super.onPause();
        unregisterReceiver(mBroadcastReceiver);
    }
}

Main Fragment to generate multiple fragments with summary like this :

public class NotificationsFragment extends Fragment {

    private static final int REQUEST_CODE = 2323;

    private static final String NOTIFICATION_TYPE =
            "notification_type";

    private static final int NOTIFICATION_GROUP_ID = 1;

    private NotificationManager mNotificationManager;

    private TextView tvTotalNotifications;

    private static int sNotificationId = NOTIFICATION_GROUP_ID + 1;

    private PendingIntent mDeletePendingIntent;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_notification_builder, container, false);
    }

    @Override
    public void onResume() {
        super.onResume();
        updateNotifications();
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        mNotificationManager = (NotificationManager) getActivity().getSystemService(
                Context.NOTIFICATION_SERVICE);

        tvTotalNotifications = (TextView) view.findViewById(R.id.tvTotalNotifications);

        view.findViewById(R.id.add_notification).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                updateNotificationAndSummaries();
            }
        });

        //creating pending intent that will fire whenever user will generate any notificaiton.

        Intent deleteIntent = new Intent(ActiveNotificationsActivity.ACTION_NOTIFICATION_DELETE);
        mDeletePendingIntent = PendingIntent.getBroadcast(getActivity(),
                REQUEST_CODE, deleteIntent, 0);
    }

    private void updateNotificationAndSummaries() {

        //create first time notification in notification bar only setting group type, later we will set group summary and ll update notifications.
                
        final NotificationCompat.Builder builder = new NotificationCompat.Builder(getActivity())
                .setSmallIcon(R.mipmap.ic_notification)
                .setContentTitle(getString(R.string.app_name))
                .setContentText(getString(R.string.sample_notification_content))
                .setAutoCancel(true)
                .setDeleteIntent(mDeletePendingIntent)
                .setGroup(NOTIFICATION_TYPE);

        final Notification notification = builder.build();
        mNotificationManager.notify(getNewNotificationId(), notification);
        updateSummary();
        updateNotifications();
    }

    protected void updateSummary() {

        // StatusBarNotification store total number of active notifications we can get it from Notification manager get Active notificaiton method and then can get its length to identify total notifications.

        final StatusBarNotification[] activeNotifications = mNotificationManager
                .getActiveNotifications();
        int numberOfNotifications = activeNotifications.length;
        for (StatusBarNotification notification : activeNotifications) {
          if (notification.getId() == NOTIFICATION_GROUP_ID) {
            numberOfNotifications--;
            break;
          }
        }
        // if we have more than 1 notifications then we can set some summary type on it and group.

        if (numberOfNotifications > 1) {
            String notificationContent = "Active notifiations are :" + numberOfNotifications;
            final NotificationCompat.Builder builder = new NotificationCompat.Builder(getActivity())
                    .setSmallIcon(R.mipmap.ic_notification)
                    .setStyle(new NotificationCompat.BigTextStyle()
                            .setSummaryText(notificationContent))
                    .setGroup(NOTIFICATION_TYPE)
                    .setGroupSummary(true);
            final Notification notification = builder.build();
            mNotificationManager.notify(NOTIFICATION_GROUP_ID, notification);
        } else {
            mNotificationManager.cancel(NOTIFICATION_GROUP_ID);
        }
    }

    protected void updateNotifications() {

        // StatusBarNotification store total number of active notifications we can get it from Notification manager get Active notificaiton method and then can get its length to identify total notifications.

        final StatusBarNotification[] activeNotifications = mNotificationManager
                .getActiveNotifications();
        final int numberOfNotifications = activeNotifications.length;
        tvTotalNotifications.setText(getString(R.string.active_notifications,
                numberOfNotifications));
    }


    public int getNewNotificationId() {
        int notificationId = sNotificationId++;

        if (notificationId == NOTIFICATION_GROUP_ID) {
            notificationId = sNotificationId++;
        }
        return notificationId;
    }
}