带有树视图的组合框

I have a combobox which when clicked will show a treeview in the drop down. In the displayed tree view you can check and uncheck treeview items. But when I double click on treeview items I am getting a part of tree view displayed in the editable text box of the combobox. I dont want anything to be displayed there? How to get rid of it I have a combobox which when clicked will show