Hi all, was looking for some advice. Our back slopes up towards houses behind, so we are somewhat overlooked. No real issue here, however last year neighbour behind and slightly left of us build a raised treehouse backing on to myself & next door neighbours back fence.Base of treehouse probably begins at top of our fence so raised roughly 5ft over our fence. Again no real issue, only the side of the tree house is as per below - has a balcony of sorts which means kids are hanging over, predominantly our side, as shouting into their friends next door! *I should emphasise must smaller in width than the image below but taller, image is just to explain the balcony aspect which is the real impact!*

I don't overly want to make an issue of it, but does have an impact as at times stuff get's thrown in, but mainly it scares the absolute bejasus out of our rescue dog so that's not ideal. We have artificial grass in the back half of the garden so looking to try get a tree which is more or less fully grown that I could place in back left corner. Again just to give us some privacy and hopefully as minimal impact on the treehouse or neighbours behind! Any suggestions? Would need to be roughly 6/7ft tall I imagine, with preference on low maintenance and impact on neighbours if that's possible!
Any experts with any suggestions?