private void treeView1_ItemDrag(object sender, ItemDragEventArgs e)
        {
            if (e.Button != MouseButtons.Left || (e.Item as TreeNode) == null)
                return;

            try
            {
                string[] fileList = new string[] { (e.Item as TreeNode).Text.ToString() };
                DataObject fileDragData = new DataObject(DataFormats.FileDrop, fileList);
                DoDragDrop(fileDragData, DragDropEffects.Copy);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "DragNDrop Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }