Who is responsible for tree trimming on property line?

The tree owner is responsible for the tree. It is unlikely the tree exactly straddles the line. It was probably planted on one side of the line, even if now spills over.

However, if any branches overhang the property line, the property owner can trim those branches.

Good neighbors talk it out. Yes, the branches hanging over the line can be cut off by the owner of the land they hang over, but that can kill the tree, or topple it in the next storm.
The person who doesn't like the branches hanging over has to pay for any cutting if the neighbor refuses to chip in.
There may be local ordinances in your town that add to state law, so ask, if there is a dispute.