<TreeView.ItemContainerStyle>
    <Style TargetType="{x:Type TreeViewItem}">
         <EventSetter Event="TreeViewItem.PreviewMouseLeftButtonDown" Handler="PreviewMouseLeftButtonDown" />
    </Style>
</TreeView.ItemContainerStyle>

void PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    if (sender is TreeViewItem)
    {
       //clone the tree item, create an adorner, apply adorner
       //doDragDrop
    }
}

HeaderNodeObject
   |_LeafnodeObject
   |_LeafNodeOject