After working on this and doing some research, ""Hierarchical ItemsSource" has been determined to be a new product idea. You can suggest new product ideas for future versions (or vote for existing ones) at http://ideas.infragistics.com.

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Hi,

if the ItemsSource of XamComboEditor is ObservableCollection you just need to add an item to it. If you're not using an ObservableCollection you could re set the Combo's ItemsSource to a collection containing the item you need to add.

HTH,