public DemoTreeViewDragDrop()
        {
            InitializeComponent();

            SampleTreeView.ItemsSource = BuildDepartmentTree();

            SampleTreeView.AllowDragDrop = true;
            dragDrop = new CustomDragDrop(SampleTreeView);
        }
        public DemoTreeViewDragDrop()
        {
            InitializeComponent();

            SampleTreeView.ItemsSource = BuildDepartmentTree();

            SampleTreeView.AllowDragDrop = true;
            dragDrop = new CustomDragDrop(SampleTreeView);
            SampleTreeView.DragOver += dragDrop.HandleDragOver;
            SampleTreeView.DragDrop += dragDrop.HandleDragDrop;
        }