Probably black flies, adult form of decomposing soil maggots, and nothing to worry about...other than avoiding conditions that cause them (too wet).

On a side note, a hardy fruit tree shouldn't be growing inside. They require some chilling hours and dormancy to survive more than a couple of years.

I could be black aphids.

On enlarging the picture I think black aphids too.

I'm gonna third that - aphids!!

Thank you all! I am going to attempt to treat them with neem oil and soap.

Constant,

You only have on branch of a tree with aphids, just squish them with you fingers. You can wear gloves if you want. No need to spray esp. Indoors.

You can kill aphids just by using dish soap&water only. Don't spray in the hot sun. It suffocates their bodies.