Ionic 2 Multiple Checkboxes with FormBuilder

Survey app checkbox photo

I currently faced the issue of building the form on multiple choice questions. At this moment, the form for single choice works well, only left multiple choice questions. The goal I want to have is something like this:

{
  "questions": [
    // if multiple choices question
    {
      "question_id": 17,
      "answer_ids": [81,82,83]
    },
    {
      "question_id": 20,
      "answer_ids": [101,102,104]
    }
  ]
}

survey.ts

    this.surveyForm = this.formBuilder.group({
      questions: formBuilder.array([])
    })

    for (var i = 0; i < this.questions.length; i++) {

      if(this.questions[i].question_type == '2') {
        // get multiple
        let question = formBuilder.group({
          question_id: [this.questions[i].id, Validators.required],
          answer_ids: formBuilder.array([])
        });
        this.surveyForm.controls['questions'].push(question);
        // for (var j = 0; j < this.questions[i].answers.length; j++) {
        //   console.log(j);
          // let answer = formBuilder.array(this.questions[i].answers)
          // console.log(answer)
          // this.questions[i].answers[j].push(new FormControl());
          // this.surveyForm.controls['questions'].controls['answer_ids'].push(new FormControl('', [Validators.required]))
        // };
        console.log('m')
      }
    }

survey.html

 <div *ngIf="surveyForm">
    <form [formGroup]="surveyForm">
      <div formArrayName="questions">
        <div *ngFor="let question of questions; let i = index" [formGroupName]="i" padding-bottom>
          <ion-row>
            <ion-col col-2>
              <h5>{{ i + 1 }}.</h5>
            </ion-col>
            <ion-col col-10>
              <h5>{{ question.text }}</h5>
              <p>{{ question.instruction }}</p>
              <div *ngIf="question.question_type == 1; else multiple_choice">
              <ng-template #multiple_choice>
                <ion-list formArrayName="answer_ids">
                  <div *ngFor="let choice of question.answers; let i = index">
                    <ion-item>
                      <ion-label style="white-space: normal;">{{ choice.id }}</ion-label>
                      <ion-checkbox (ionChange)="onChange(choice.id, $event._checked)" value="choice.id"></ion-checkbox>
                    </ion-item>
                  </div>
                </ion-list>
              </ng-template>
            </ion-col>
          </ion-row>
        </div>
      </div>
    </form>
  </div>

What could be the best way that I can get the value id from each multiple choice checkbox to push into the array of specific question?