I got one of those key lime trees as a gift. It's in a small planter. The
instructions say to prune it to make it bushier if I want. However, I don't
know what to prune. It's about 9 inches tall. There is one branch going off
the side. There are leaves all the way up the "Y" split.

Should I trim back the tall part? If so, how much? If not, then when do I
prune and where?

Much obliged for the feedback.