How to select suboccurrence via API ?

When i run this code

SolidEdgeFramework.SelectSet SS=Application.ActiveSelectSet;
SS.Add(Occ); //Occ is SolidEdgeAssembly.Occurrence object
SS.Add(SubOcc); //SubOcc is SolidEdgeAssembly.Suboccurrence object

i get result:

Occ is selected.
SubOcc is not selected.

Thanks.