So the blokes a nutter your mates too scared to ask him about the tree, your mate takes the advice to kill the tree. Now said nutter finds the tree poisoned what do you think he’ll then do.
i. Think wow the neighbours shafted me oh well didn’t like the tree anyway he’s done me a favour i’ll go round and thank him.
ii. Think i loved that tree i did but hey that neighbour may kick my face in so best not say anything.
iii. Think i’ve been shafted by neighbour think i’ll go round it kick ten bells out of him and continue to do this weekly until he moves.
Pick one but i’ll bet it’s going to be iii.
Good Luck for your mate though neighbour disputes just fester and get worse IME