问WPF - ListBox异步绑定到具有动画的项

EN

<TreeView Grid.Row="2" x:Name="LevelObjects"
    Style="{StaticResource TreeViewStyle}"
    ItemsSource="{Binding Path=Items, IsAsync=True}" >...

private ObservableCollection<LevelTreeItemViewModel> items;
    public ObservableCollection<LevelTreeItemViewModel> Items
    {
        get 
        {
            if (items == null)
            {
                items = GetLevelObjects();
            }
            return items; 
        }
    }