How to use the @angular/material.MatTreeFlatDataSource function in @angular/material

private transformer = (node: ExtendedMenu, level: number) => {
        return {
            expandable: !!node.subMenus && node.subMenus.length > 0,
            name: node.displayName,
            level,
            id: node.id,
            extMenu: node
        };
    }

    treeControl = new FlatTreeControl(
        node => node.level, node => node.expandable);
    treeFlattener = new MatTreeFlattener(
        this.transformer, node => node.level, node => node.expandable, (node: ExtendedMenu) => node.subMenus);

    dataSource = new MatTreeFlatDataSource(this.treeControl, this.treeFlattener);
    hasChild = (_: number, node: MenuNode) => node.expandable || node.level === 0;

    ngOnInit(): void {
        this.pageService.init('menus').subscribe()
        this.app = this.activetedRouter.snapshot.data.app
        this.menus = this.app.menus as ExtendedMenu[]
        this.dataSource.data = this.menus
    }

    ngAfterViewInit(): void {
        // Ensure we have nested node with more than 1
        if(this.menus.some(a => ObjectUtils.isNotNull(a.subMenus) && a.subMenus.length > 0)){
            this.tree.treeControl.expandAll()
        }
    }

extMenu: node,
            checked: isChecked
        }
        if(isChecked){
            this.checklistSelection.select(menuNode)
        }

        return menuNode;
    }

    treeControl = new FlatTreeControl(
        node => node.level, node => node.expandable);
    treeFlattener = new MatTreeFlattener(
        this.transformer, node => node.level, node => node.expandable, (node: ExtendedMenu) => node.subMenus);

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

    checklistSelection = new SelectionModel(true)
    menuProfile: MenuProfile

    
    hasChild = (_: number, node: MenuNode) => node.expandable || node.level === 0;

    ngOnInit(): void {
    }

    onRoleChange() {
        // Refill the claim list based on role
        this.menuProfile = _.find(this.app.menuProfiles, profile => profile.role === this.selectedRole)
        if (this.menuProfile) {

        }

this.flat_node_map[node.id] = res;
        return res;
    };

    get_children = node => ofObservable(node.children);

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

    treeFlattener = new MatTreeFlattener(
        this.transformer,
            node => node.level,
            node => node.expandable,
        this.get_children);

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

    load() {
        let self = this;
        this.service.steps(this.task).subscribe(res => {
            if(!res || !res.data){
                return;
            }
            self.dataSource.data = res.data;
            self.treeControl.expandAll();

        });
    }

    ngOnInit() {
        this.load();

private init() {
    this.recordDatasource = new MatTreeFlatDataSource(this.triumphTreeControl, this.treeFlattener2);
    this.recordDatasource.data = this.player.records;
    this.filterTriumphs();
    this.setTrackedTriumphs();
    this.seasonIndex = 0;
    if (this.selectedTab === 'triumphs') {
      if (this.selectedTreeNodeHash != null) {
        for (const n of this.triumphTreeControl.dataNodes) {
          if (n.data.hash === +this.selectedTreeNodeHash) {
            this.triumphTreeControl.expand(n);
            this.expandParents(this.triumphTreeControl, n);
            break;
          }
        }
      }
    }
  }

level,
            expandable: !!node.subClaims && node.subClaims.length > 0,
            parentId: node.parentId
        }

        return claimNode;
    }

    selectedRolePortalClaims: RolePortalClaimModel[] = []
    selectedClaims: SelectablePortalClaim[] = []
    treeSelectedControl = new FlatTreeControl(
        node => node.level, node => node.expandable);
    treeSelectedFlattener = new MatTreeFlattener(
        this.transformerSelectedClaim, node => node.level, node => node.expandable, (node: SelectablePortalClaim) => node.subClaims);

    dataSourceSelectedClaims = new MatTreeFlatDataSource(this.treeSelectedControl, this.treeSelectedFlattener);
    
    hasChild = (_: number, node: ClaimNode) => node.expandable || node.level === 0;    

    ngOnInit(): void {
        this.pageService.init('role-claims').subscribe()
        this.activatedRoute.paramMap.subscribe(params => {
            this.selectedRole = params.get('roleName')
        })
        this.selectedRolePortalClaims = this.activatedRoute.snapshot.data.roleClaims

        this.logger.debug('selected claims', this.selectedRolePortalClaims)
        combineLatest(this.pagesClient.getAllPortalClaims(), this.appClient.getAllApps(), (v1, v2) => ({ v1, v2 })).subscribe(
            pair => {
                const allclaims: SelectablePortalClaim[] = []
                const appClaim: SelectablePortalClaim = {
                    name: 'apps',

if (!!found) {
                claimNode.checked = found.claims.indexOf(claimNode.id) > -1
                if (claimNode.checked) {
                    this.checklistSelection.select(claimNode)
                }
            }
        }

        return claimNode;
    }
    treeControl = new FlatTreeControl(
        node => node.level, node => node.expandable);
    treeFlattener = new MatTreeFlattener(
        this.transformer, node => node.level, node => node.expandable, (node: SelectablePortalClaim) => node.subClaims);

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

    allPortalClaims: SelectablePortalClaim[] = []
    checklistSelection = new SelectionModel(true)

    private transformerSelectedClaim = (node: SelectablePortalClaim, level: number) => {
        const claimNode: ClaimNode = {
            id: node.name,
            name: node.displayName,
            checked: false,
            level,
            expandable: !!node.subClaims && node.subClaims.length > 0,
            parentId: node.parentId
        }

        return claimNode;
    }

constructor(database: ConfigDb) {
    this.treeFlattener = new MatTreeFlattener(this.transformer, this._getLevel,
        this._isExpandable, this._getChildren);
    this.configTreeControl = new FlatTreeControl(this._getLevel, this._isExpandable);
    this.configDataSource = new MatTreeFlatDataSource(this.configTreeControl, this.treeFlattener);

    database.dataChange.subscribe(data => this.configDataSource.data = data);
  }

takeUntil(this.unsubscribe$)).subscribe(p => {
        this.recordDatasource = new MatTreeFlatDataSource(this.triumphTreeControl, this.treeFlattener2);
        this.recordDatasource.data = p.records;
        CollectionTreeComponent.expandToSelected(this.selectedTreeNodeHash, this.triumphTreeControl);
      });

this.state.player.pipe(first()).subscribe(p => {
      this.collectionDatasource = new MatTreeFlatDataSource(this.collectionTreeControl, this.treeFlattener2);
      this.collectionDatasource.data = p.collections;
      CollectionTreeComponent.expandToSelected(this.selectedTreeNodeHash, this.collectionTreeControl);
    });
  }