private void addAction(NotificationCompat.Builder builder, Action action) {
        Intent actionClickIntent = new Intent(context, NotificationClickActivity.class)
            .putExtra(Notification.EXTRA_ID, options.getId())
            .putExtra(Action.EXTRA_ID, action.getId())
            .putExtra(Options.EXTRA_LAUNCH, action.isLaunchingApp())
            .setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_NO_HISTORY);

        PendingIntent actionClickPendingIntent = PendingIntent.getActivity(context,
            // Each action intent have to get a unique request code, so they don't overwrite each other
            Manager.getRandomRequestCode(),
            actionClickIntent, PendingIntent.FLAG_MUTABLE | PendingIntent.FLAG_UPDATE_CURRENT);

        NotificationCompat.Action.Builder actionBuilder = new NotificationCompat.Action.Builder(
                action.getIcon(), action.getTitle(), actionClickPendingIntent);

        if (action.isWithInput()) actionBuilder.addRemoteInput(action.buildRemoteInput());

        builder.addAction(actionBuilder.build());
    }
Add an action to the builder.
src/android/Notification.java