No, this is The Maven's arena, you fight map bosses here from 4 at a time to 10 at a time then eventually you can fight The Maven herself.

is this the shaper hide out, or actual shaper arena, maybe? I've not been that far yet. Just doing my Atlas, for the first time. I did maps back in 2016, but we didn't have atlas back then (or if we did, it looked nothing like the tree we have today)