In my case:
[curt:misc]$ mdls -name kMDItemContentTypeTree U.scala kMDItemContentTypeTree = ( "dyn.ah62d4rv4ge81g25brvuu", "public.item", "dyn.ah62d4rv4ge81g25brvuu", "public.data" )
public.source-code is not in the list. How can I add it to the list of Content Types?