public sealed partial class MainWindow : Window
    {
        private readonly List<ColorItem> RedItems = ColorItem.Create<RedItem>(3);
        private readonly List<ColorItem> GreenItems = ColorItem.Create<GreenItem>(3);

        public MainWindow() => InitializeComponent();
        private void UpdateTreeView(List<ColorItem> items) => TreeView.ItemsSource = items;
        private void RedItems_Click(object sender, RoutedEventArgs e) => UpdateTreeView(RedItems);
        private void GreenItems_Click(object sender, RoutedEventArgs e) => UpdateTreeView(GreenItems);
        private void Clear_Click(object sender, RoutedEventArgs e) => UpdateTreeView(null);
    }

    public class ColorItem
    {
        public List<ColorItem> Children { get; set; }
        public override string ToString() => GetType().Name;

        public static List<ColorItem> Create<T>(int childCount) where T : ColorItem, new()
        {
            var items = new List<ColorItem>();
            for (int i = 1; i <= childCount; i++)
            {
                var item = new T();
                item.Children = Create<T>(childCount - 1);
                items.Add(item);
            }
            return items;
        }

    }
    public class RedItem : ColorItem { }
    public class GreenItem : ColorItem { }

    public class ColorItemTemplateSelector : DataTemplateSelector
    {
        public DataTemplate RedItemTemplate { get; set; }
        public DataTemplate GreenItemTemplate { get; set; }

        protected override DataTemplate SelectTemplateCore(object item)
        {
            return item switch
            {
                RedItem => RedItemTemplate,
                GreenItem => GreenItemTemplate,
                _ => null
            };
        }
    }