in docs-content/examples-source/material/tree/tree-checklist/tree-checklist-example.ts [132:145]
constructor(private _database: ChecklistDatabase) {
this.treeFlattener = new MatTreeFlattener(
this.transformer,
this.getLevel,
this.isExpandable,
this.getChildren,
);
this.treeControl = new FlatTreeControl<TodoItemFlatNode>(this.getLevel, this.isExpandable);
this.dataSource = new MatTreeFlatDataSource(this.treeControl, this.treeFlattener);
_database.dataChange.subscribe(data => {
this.dataSource.data = data;
});
}