<activity android:name="MainActivity" android:launchMode="singleInstance".....

<activity android:name="some.long.package.from.a.library.NotificationActivity" android:noHistory="true" android:launchMode="singleInstance" android:parentActivityName=".MainActivity">
  <meta-data android:name="android.support.PARENT_ACTIVITY" android:value=".MainActivity"/>
</activity>

Intent intent = new Intent(context, NotificationActivity.class);
 PendingIntent pendingIntent = TaskStackBuilder.create(context)
                .addNextIntentWithParentStack(intent)
                .getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);