I had some tables which just had one groupping, and the arrow (accordion-type) was working fine, and users understood perfectly. (As for now, I was using option B/groupping1).
Now, we have to introduce double groupping, which means that arrows might not be as userfriendly/easy to understand as they were, and specially in that position. What do you think works best, or do you have any other options in mind?
Thanks in advance