it sounds like you and the neighbor have a history of being hostile with one another and criticizing how the other handles things on their property.
I have been nothing but nice to them. We were outside talking, being neighborly when the tree and other plants were being delivered. I asked where it was all going since the front of their house has very pretty azaleas, butterfly bush, and some holly bushes. They never really told me where the bushes were going just where the tree was going to be put. I mentioned don't you think that is a little close to the property line? That is when I got the response that I did. Never was ugly with them and have never done anything that would interfere/harm their property.
Personally, I cannot imagine this kind of angst over a tree (unless it were a tree that was about to fall onto my roof or something).
The city approve a zoning change to change the "green space only" zoned area right behind my house. Next summer a 30 meter tall building with 12 studio apartments (aimed at students) will be built 10 cm from my back fence (we have a small yard too--this is maybe 15 meters from my house). I am upset by that--but not more so than you seem to be by a TREE
Wow! Rezoning a green space only for apartments. Yes, I would imagine you being upset with that. Did residents get to speak out about the change?
Now THAT is unacceptable and you have every right to be annoyed by it.