Yii2 dependent dropdownlist for multiple dropdownlist

I have this model:

    public function attributeLabels()
{
    return [
        'exam_id' => Yii::t('aca', 'Exam ID'),
        'exam_exam_group_id' => Yii::t('aca', 'Exam Group'),
        'exam_group_year_id' => Yii::t('aca', 'Academic Year'),
        'exam_group_term_id' => Yii::t('aca', 'Academic Term'),
        'exam_group_class_group_id' => Yii::t('aca', 'Class Group'),
        'exam_group_class_id' => Yii::t('aca', 'Class'),
        'exam_group_class_arm_id' => Yii::t('aca', 'Class Arm'),
        'exam_group_subject_id' => Yii::t('aca', 'Subject'),

    ];
}

and DependentController

	public function actionGetclassarm($id)
{
	$rows = \app\modules\academic\models\AcaClassArms::find()->where(['class_arm_class_id' => $id,'is_status'=>0])->all();	 
	echo "<option value=''>".Yii::t('app', '--- Select Class Arm ---')."</option>";	 
	if(count($rows)>0){
	    foreach($rows as $row){
	        echo "<option value='$row->class_arm_id'>$row->class_arm_name</option>";
	    }
	}
	else{
	    echo "";
	} 
    } 

View

                    <?= $form->field($model, 'exam_group_class_id')->widget(Select2::classname(), [
                    'data' => ArrayHelper::map(\app\modules\academic\models\AcaClassMaster::find()->where(['is_status' => 0])->all(),'class_id','class_name','classGroups.class_group_name'),
                    'language' => 'en',
                    'options' => ['placeholder' => '--- Select Class ---', 
                        'onchange'=>'
                            $.get( "'.Url::toRoute('dependent/getclassarm').'", { id: $(this).val() } )
                                .done(function( data ) {
                                    $( "#'.Html::getInputId($model, 'exam_group_class_arm_id').'" ).html( data );
                                }
                            );' 
                    ],
                    'pluginOptions' => [
                        'allowClear' => true
                    ],
                ]); ?>

I want the dropdownlist above to load two other dropdownlists. Am only able to load one as shown below:

                    <?= $form->field($model, 'exam_group_class_arm_id')->widget(Select2::classname(), [
                'data' => ArrayHelper::map(\app\modules\academic\models\AcaClassArms::findAll(['class_arm_id' => $model->exam_group_class_arm_id]),'class_arm_id','class_arm_name'),
                    'language' => 'en',
                    'options' => ['placeholder' => '--- Select Class Arm ---'],
                    'pluginOptions' => [
                        'allowClear' => true
                    ],
                ]); ?>

Am unable to load the second dropdownlist that is shown below

exam_group_subject_id

for
app\modules\academic\models\AcaSubjects

How do I achieve this.

Thanks

Maybe you can use something like http://demos.krajee.com/widget-details/depdrop.
I did not use it in practice, but it looks good. Good luck.