How to collapse all nodes on SliverTreeView when tree data loaded in Flutter Animated Tree View Module

I am using animated_tree_view SliverTreeView widget to make a tree view. This widget expands all of the nodes when it finished loading. This is my current code.

SliverTreeView.simple(
    tree: simpleTree,
    expansionBehavior: ExpansionBehavior.collapseOthers,
    showRootNode: false,
    key: _simpleTreeKey,
    onTreeReady: (controller) {
      controller.collapseNode(simpleTree);
    },
    scrollController: scrollController,
    builder: (context, node) => Card(
        child:
            node.isRoot ? buildRootItem(node) : buildListItem(node)),
  ),

To make it myself, I tried to use onTreeReady method called when it loaded. But it is not working now. If you have experience in SliverTreeView, please help me.

I solved this issue myself by making the treeview with FutureBuilder.

The result

final Future<TreeNode> futureTree = Future<TreeNode>.delayed(
    const Duration(milliseconds: 1000),
    () => ActivityModel().getTree(),
  );

FutureBuilder<TreeNode>(
            future: futureTree,
            builder: (BuildContext context, AsyncSnapshot<TreeNode> snapshot) {
              if (snapshot.hasData) {
                return CustomScrollView(
                  controller: scrollController,
                  slivers: [
                    SliverToBoxAdapter(
                      child: Padding(
                          padding: const EdgeInsets.only(
                              top: 12.0, left: 12, right: 30, bottom: 12),
                          child: Align(
                            alignment: Alignment.topLeft,
                            child: SizedBox(
                              width: 200,
                              height: 40,
                              child: ElevatedButton(
                                child: const Text("Add main activity"),
                                style: ElevatedButton.styleFrom(
                                    backgroundColor:
                                        Theme.of(context).primaryColor,
                                    textStyle:
                                        const TextStyle(color: Colors.white),
                                    shape: RoundedRectangleBorder(
                                        borderRadius:
                                            BorderRadius.circular(5))),
                                onPressed: () {
                                  // simpleTree.add(TreeNode());
                                  Navigator.of(context)
                                      .push(MaterialPageRoute(
                                          builder: (context) =>
                                              const ActivityAdd(
                                                  title: 'Add Activity',
                                                  selfId: 'root')))
                                      .then((val) => {
                                            val == 'success'
                                                ? _getRequests()
                                                : null
                                          });
                                },
                              ),
                            ),
                          )),
                    ),
                    SliverTreeView.simple(
                        tree: simpleTree,
                        expansionBehavior: ExpansionBehavior.collapseOthers,
                        showRootNode: false,
                        key: _simpleTreeKey,
                        onItemTap: (value) => {},
                        scrollController: scrollController,
                        onTreeReady: (controller) => {debugPrint("Loaded")},
                        builder: (context, node) {
                          return node.isRoot
                              ? buildRootItem(node)
                              : buildListItem(node);
                        }),
                  ],
                );
              } else if (snapshot.hasError) {
                return Text('Error: ${snapshot.error}');
              } else {
                return Center(
                  child: SizedBox(
                    width: 60,
                    height: 60,
                    child: CircularProgressIndicator(),
                  ),
                );
              }
            })