private void listViewDemo_DragDrop(object sender, DragEventArgs e)
        {
            if (!is_listview) //treeview item
            {
                //get a text of a draged item
                string str = e.Data.GetData(DataFormats.Text).ToString();
                //get information about hovered item
                ListViewHitTestInfo hit_info = listViewDemo.HitTest(listViewDemo.PointToClient(new Point(e.X, e.Y)));
                //check position - must be on an item
                if (hit_info.Location == ListViewHitTestLocations.None) return;
                ListViewItem prev_item = hit_info.Item;
                ListViewGroup group = prev_item.Group;
                int idx = prev_item.Index;
                //create a new key
                Guid key = Guid.NewGuid();
                string item_key = key.ToString();
                //create a new item
                //option 1
                if (idx == 0)
                {
                    group.Items.Insert(idx, listViewDemo.Items.Add(item_key, str, ""));
                }
                else
                {
                    group.Items.Insert(idx - 1, listViewDemo.Items.Add(item_key, str, ""));
                }
               
                //option2
                //group.Items.Insert(idx, listViewDemo.Items.Add(item_key, str, ""));
            }
        }