Select the entities to add to the subgroup. If you use the Single selection method and select previously grouped entities, you can reassign the entities to the new group, using one of three selection options:
Group – This setting creates one new group for each group that contains at least one selected entity. Each new group has the same subgroup structure as the original group, except that it does not contain empty subgroups.
Subgroup – This setting creates one new subgroup for each selected entity.
Entity – This setting un-groups all selected entities.