OK so...If I am reading this right...these trees are a concern to you. And since they are between your driveways, obviously a concern during storms to him. Sounds like he did everyone a favor and maybe avoided future problems such as if limbs or the trees came down on his cars or yours. The real issue seems that the tree company did not remove the trees after they cut them down. To me, would be a total dick move to lawyer up or even get upset yet. Yeah, he should have called you. What I would do is walk over there, talk to the guy...Explain that while appreciated, you think he should have called you first so that you and your wife were not surprised. And then ask what is going to be done with the trees that have been cut down. Maybe the tree company is coming back for them. I have a seen a lot of times after storms in the winter, they are so busy working truly dangerous fells that cutting is first priority for everyone and then coming back to cleanup happens later when things calm down. Anyway- ask him...also talk to him that though you had also thought of doing this, you just were not in position financially to do so and why you held off. Since he did this on his own without asking, he should not expect you to pay but it is still good on your part to offer that you do realize it did cost. If he is planning to use some of the wood for firewood, maybe offer him some good will that you can help him cut it, stack it.
Bottomline, you be the good guy, you may find that he is too. Worst case, he is a complete jerkoff and you end up not talking, which you dont now anyway. But at least you know you did everything you could.