How to drag and drop elements from treeview in WPF Diagram (SfDiagram)?

//Adding ItemDragStarting event. 
sftreeview.ItemDragStarting += Sftreeview_ItemDragStarting;
//Method to execute ItemDragStarting event.
private void Sftreeview_ItemDragStarting(object sender, TreeViewItemDragStartingEventArgs e)
{
    DragObject<TreeViewNode> dataObject = new DragObject<TreeViewNode>(e.DraggingNodes.First() as TreeViewNode);
    DragDrop.DoDragDrop(sender as DependencyObject, dataObject, DragDropEffects.Copy);
 
    //This e.Cancel is used to stop the position changes in treeview
    e.Cancel = true;
}

//Creating SfDiagram instance with nods and connectors collection.
SfDiagram diagram = new SfDiagram()
{
    Nodes = new NodeCollection(),
    Connectors = new ConnectorCollection(),
};
 
//Adding DragEnter event.
(diagram.Info as IGraphInfo).DragEnter += MainWindow_DragEnter;
//Method to execute DragEnter event.
private void MainWindow_DragEnter(object sender, ItemDropEventArgs args)
{
    // args.Source have the data which is dragged for drop.
    if (args.Source is DataObject)
    {
        object dataObject = (args.Source as DataObject).GetData(typeof(DragObject<TreeViewNode>));
        TreeViewNode treeViewItem = (dataObject as DragObject<TreeViewNode>).Source;
    }
}

//Method to execute DragEnter event.
private void MainWindow_DragEnter(object sender, ItemDropEventArgs args)
{
    // args.Source have the data which is dragged for drop.
    if (args.Source is DataObject)
    {
        object dataObject = (args.Source as DataObject).GetData(typeof(DragObject<TreeViewNode>));
        TreeViewNode treeViewItem = (dataObject as DragObject<TreeViewNode>).Source;
 
        // Based on the TreeView Item you can add different types of Node.              
        if (treeViewItem.Level.ToString() == "0")
        {
            args.Source = new NodeViewModel()
            {
                UnitHeight = 40,
                UnitWidth = 120,
                Shape = this.Resources["Rectangle"],
                ShapeStyle = this.Resources["Level1NodeStyle"] as Style,
                Annotations = new AnnotationCollection()
                {
                     new AnnotationEditorViewModel()
                     {
                          Content = treeViewItem.Content.ToString(),
                          Offset = new Point(0,0),
                          Margin = new Thickness(23,10,0,0),
                     },
                },
            };
        }
    }
}

//Adding ItemDrop event.
(diagram.Info as IGraphInfo).ItemDropEvent += MainWindow_ItemDropEvent;
 
//Method to execute ItemDropEvent.
private void MainWindow_ItemDropEvent(object sender, ItemDropEventArgs args)
{
    if (args.Source is INode)
    {
        INode item = args.Source as INode;
        //Getting position of dropped node.
        double offsetX = item.OffsetX;
        double offsetY = item.OffsetY;
    }
}