By default, in your editor items that contain child items are collapsed. Use the ExpandAll method to expand all items in the editor. Use the InsertItem method to insert child items. Use the AddItem method to add predefined values to a drop down type editor. Use the ExpandItem method to expand a predefined value. Call the ExpandAll method after inserting the items. Use the SortItems method to sort the items in a drop down editor.

The following screen show shows a simple hierarchy into a built-in DropDownList editor: