A question about the tree associated with a git notes commit

Is the tree associated with a notes commit limited to a single level,
or is there some attempt to balance the tree as the number of
annotated objects increases?

If the tree is currently restricted to a single level, is this
eventually going to be a problem as the number of annotated objects
continues to grow?

Apologies if this question is answered with trivial analysis of the
code, I admittedly haven't done that.

jon.