Groups the atlas's own subcategory entities, the grouping nodes EntryCards.GroupBySub renders a browse page's headings from, one tree per major type: psychologist, theory, study, school and psychological-phenomenon are each subdivided by branch or by a documented editorial scheme. The grouping comes from the subcategory type rather than from subject matter; a subcategory node is structural scaffolding, not a psychological subject in its own right. It deliberately excludes the member entities a subcategory groups, filed under their own type's category, and the branch type itself, which is the classification axis these trees are built from rather than a type that gets subcategorized in turn.