How to add new values to multiple Select2 from Kartik instead of replace old ones?

Question

I use Select2 widget in multiply mode in YII2 framework. "kartik-v/yii2-widget-select2": "@dev" - this one I have downloaded via composer.

kartik-v/yii2-widget-select2 dev-master dd09e46

I added initial values with ajax on widget init ('initSelection'). And added another ajax method to suggest new values on user's typing. When user select one from list, it replaced initial values what were added on init. New values replace initial values, but don't another new. I want new values to add to initial instead of replace it.

<?= $form->field($model, 'security[]')->widget(Select2::class, [

                    'attribute'     => 'security',
                    'hideSearch'    => true,
                    'data'=>$security_data,
                    'options'       => [
                        'placeholder' => 'Security',
                        'multiple'    => true,
                    ],
                    'pluginOptions' => [
                        'allowClear'         => true,
                        'minimumInputLength' => 1,
                        'ajax'               => [
                            'url'      => Url::toRoute([ '/admin/security/select-items' ]),
                            'dataType' => 'json',
                            'data'     => new JsExpression('function(params) { return {q:params.term}; }'),
                            'results' => new JsExpression('function(data,page) { return {results:data.results}; }'),
                        ],
                        'initSelection'      => new JsExpression('function(element, callback) { var id = '.Yii::$app->request->getQueryParams()['id'].';if(id !== "") {$.ajax("' . \yii\helpers\Url::toRoute([ '/admin/security/init-items' ]) . '", {data: {id: id},dataType: "json"}).done(function(data) {callback(data.results);});}}'),
                    ],
                ]); ?>

And here is my api methods:

 public function actionSelectItems($q = null){

    Yii::$app->response->format = Response::FORMAT_JSON;

    $out = ['results' => []];
   if(!empty($q)){
       $items = Security::find()->where(['like', 'title', $q])->all();
       foreach ($items as $item){
           $out['results'][] = ['id'=>$item->id, 'text'=>$item->title];

       }
   } 

    return $out;
}

public function actionInitItems($id = null){

    Yii::$app->response->format = Response::FORMAT_JSON;

    $adv = Adv::findOne($id);
    $security = @json_decode($adv->security, true);
    $out = ['results' => []];
    foreach ($security as $item){
        $text = Security::findOne($item)->title;
        $out['results'][] = ['id'=>$item, 'text'=>$text];
    }
    return $out;
}

Is there some sort of settings or I missed something when handle http result?