How to use the @dynatrace/barista-components/core.DtTreeFlattener function in @dynatrace/barista-components

constructor() {
    this.treeControl = new DtTreeControl(
      this._getLevel,
      this._isExpandable,
    );
    this.treeFlattener = new DtTreeFlattener(
      this.transformer,
      this._getLevel,
      this._isExpandable,
      this._getChildren,
    );
    this.treeTableDataSource = new DtTreeDataSource(
      this.treeControl,
      this.treeFlattener,
    );
    this.treeTableDataSource.data = TESTDATA;
  }

constructor() {
    this.treeControl = new DtTreeControl(
      this._getLevel,
      this._isExpandable,
    );
    this.treeFlattener = new DtTreeFlattener(
      this.transformer,
      this._getLevel,
      this._isExpandable,
      this._getChildren,
    );
    this.dataSource = new DtTreeDataSource(
      this.treeControl,
      this.treeFlattener,
    );
    this.dataSource.data = TESTDATA;
  }

constructor() {
    this.treeControl = new DtTreeControl(
      this._getLevel,
      this._isExpandable,
    );
    this.treeFlattener = new DtTreeFlattener(
      this.transformer,
      this._getLevel,
      this._isExpandable,
      this._getChildren,
    );
    this.dataSource = new DtTreeDataSource(
      this.treeControl,
      this.treeFlattener,
    );
    this.dataSource.data = TESTDATA;
  }

constructor() {
    this.treeControl = new DtTreeControl(
      this._getLevel,
      this._isExpandable,
    );
    this.treeFlattener = new DtTreeFlattener(
      this.transformer,
      this._getLevel,
      this._isExpandable,
      this._getChildren,
    );
    this.dataSource = new DtTreeDataSource(
      this.treeControl,
      this.treeFlattener,
    );
    this.dataSource.data = TESTDATA;
  }

constructor() {
    this.treeControl = new DtTreeControl(
      this._getLevel,
      this._isExpandable,
    );
    this.treeFlattener = new DtTreeFlattener(
      this.transformer,
      this._getLevel,
      this._isExpandable,
      this._getChildren,
    );
    this.dataSource = new DtTreeDataSource(
      this.treeControl,
      this.treeFlattener,
    );
    this.dataChange.next(TESTDATA);

    this.dataChange.subscribe(data => {
      this.dataSource.data = data;
    });
  }

constructor() {
    this.treeControl = new DtTreeControl(
      this._getLevel,
      this._isExpandable,
    );
    this.treeFlattener = new DtTreeFlattener(
      this.transformer,
      this._getLevel,
      this._isExpandable,
      this._getChildren,
    );
    this.dataSource = new DtTreeDataSource(
      this.treeControl,
      this.treeFlattener,
    );
    this.dataSource.data = TESTDATA;
  }

[data]="row"
        class="customRowClass"
      >
    
  `,
})
class SimpleDtTreeTableApp {
  getLevel = (node: TestData) => node.level;
  isExpandable = (node: TestData) => node.children.length > 0;
  getChildren = (node: TestData) => node.observableChildren;
  transformer = (node: TestData, level: number) => {
    node.level = level;
    return node;
  };

  treeFlattener = new DtTreeFlattener(
    this.transformer,
    this.getLevel,
    this.isExpandable,
    this.getChildren,
  );

  treeControl = new DtTreeControl(this.getLevel, this.isExpandable);

  dataSource = new DtTreeDataSource(this.treeControl, this.treeFlattener);

  underlyingDataSource = new FakeDataSource();

  @ViewChild(DtTreeTable, { static: true }) tree: DtTreeTable;

  constructor() {
    this.underlyingDataSource.connect().subscribe(data => {

constructor() {
    this.treeControl = new DtTreeControl(
      this._getLevel,
      this._isExpandable,
    );
    this.treeFlattener = new DtTreeFlattener(
      this.transformer,
      this._getLevel,
      this._isExpandable,
      this._getChildren,
    );
    this.dataSource = new DtTreeDataSource(
      this.treeControl,
      this.treeFlattener,
    );
    this.dataSource.data = TESTDATA;
  }

constructor() {
    this.treeControl = new DtTreeControl(
      this._getLevel,
      this._isExpandable,
    );
    this.treeFlattener = new DtTreeFlattener(
      this.transformer,
      this._getLevel,
      this._isExpandable,
      this._getChildren,
    );
    this.dataSource = new DtTreeDataSource(
      this.treeControl,
      this.treeFlattener,
    );
    this.dataSource.data = TESTDATA;
  }

`,
})
class DtTreeTableWithNullOrUndefinedChild {
  private transformer = (node: FoodNode, level: number) => ({
    expandable: !!node.children,
    name: node.name,
    level,
  });

  treeControl = new DtTreeControl(
    node => node.level,
    node => node.expandable,
  );

  treeFlattener = new DtTreeFlattener(
    this.transformer,
    node => node.level,
    node => node.expandable,
    node => node.children,
  );

  dataSource = new DtTreeDataSource(
    this.treeControl,
    this.treeFlattener,
    TREE_DATA,
  );

  constructor() {
    this.dataSource.data = TREE_DATA;
  }