protected override IDropDownBox CreateDropDownBox()
{
// Create the list.
var popupTree = new PopupTree { TabStopControl = m_comboTextBox };
popupTree.AfterSelect += m_tree_AfterSelect;
popupTree.BeforeSelect += m_popupTree_BeforeSelect;
popupTree.Load += m_tree_Load;
popupTree.PopupTreeClosed += m_popupTree_PopupTreeClosed;
return popupTree;
}