Не меняется expander в TreeView

Не меняется Expander при раскрытии елемента в TreeView

import 'package:flutter/material.dart';
import 'package:flutter_treeview/tree_view.dart';

void main() => runApp(USU());

TreeView tree = TreeView(
  shrinkWrap: true,
  physics: ClampingScrollPhysics(),
  controller: TreeViewController(
    children: [
      Node(
        key: "1",
        label: "Item1",
        children: [
          Node(
            key: "1.1",
            label: "Item1.1",
            children: [
              Node(
                key:"1.1.1",
                label: "Item1.1.1"
              )
            ],
          ),
        ],
      ),
    ],
  ),
);

class USU extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    MaterialApp window = new MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
          appBar: AppBar(),
          drawer: Drawer(
            child: ListView(
              padding: EdgeInsets.zero,
              children: [
                DrawerHeader(
                  decoration: BoxDecoration(
                    color: Colors.blue,
                  ),
                  child: Text("Drawer"),
                ),
                tree,
              ],
            ),
          )),
    );
    return window;
  }
}