Stackoverflow Question (Full code)

export class SubjectPlanComponent implements OnInit {
  planForm: FormGroup;
  subject: ISubject;
  themes: ITheme[];
  subthemes: ISubtheme[];
  activities: IActivity[];

  nodeDataArray = [
    { key: '1', name: 'Data Structures & Algorithms' },
    { key: '2', parent: '1', name: 'Trees' },
    { key: '3', parent: '1', name: 'Sorting' },
    { key: '4', parent: '2', name: 'Binary' },
    { key: '5', parent: '2', name: 'Red-Black' },
    { key: '6', parent: '3', name: 'Quicksort'},
    { key: '7', parent: '3', name: 'Tree Sort'},
    { key: '8', parent: '4', name: 'A1'},
    { key: '9', parent: '4', name: 'A2'},
    { key: '10', parent: '4', name: 'A3'},
    { key: '11', parent: '5', name: 'A4'},
    { key: '12', parent: '5', name: 'A5'},
    { key: '13', parent: '5', name: 'A6'},
    { key: '14', parent: '6', name: 'A7'},
    { key: '15', parent: '6', name: 'A8'},
    { key: '16', parent: '6', name: 'A9'},
    { key: '17', parent: '7', name: 'A10'},
    { key: '18', parent: '7', name: 'A11'},
    { key: '19', parent: '7', name: 'A12'}
  ];

  public model: go.Model = new go.TreeModel(this.nodeDataArray);

  constructor(protected activatedRoute: ActivatedRoute,
              protected jhiAlertService: JhiAlertService,
              protected themeService: ThemeService,
              protected subthemeService: SubthemeService,
              protected activityService: ActivityService,
              private formBuilder: FormBuilder) {
    this.planForm = this.formBuilder.group({
      studentCredits: [],
      studentMinGrade: []
    });
  }