DropDownTree

The DropDownTree control is similar to a MultiSelect, but it hosts a TreeView in the drop-down instead of a ListBox.

The DropDownTree's object model is also similar to the MultiSelect's: you can listen to the checkedItemsChanged event and set/set the selection using the checkedItems property:

Drop-Down-Tree with checkboxes

Drop-Down-Tree without checkboxes

Multi-Select