private void treeView_DragEnter(object sender, System.Windows.Forms.DragEventArgs e)
{
	try
	{
		// Item only from this form
		if(e.Data.GetDataPresent(typeof(TreeNode)) && (sender as Control).FindForm().Equals(this))
		{
			e.Effect = DragDropEffects.Move;
		}
		else
		{
			e.Effect = DragDropEffects.None;
		}
	}
	catch(Exception /*exception*/)
	{
		e.Effect = DragDropEffects.None;
	}
}