I also have a cherry tree. It's self seeded, tall as the house and produces tiny black cherries which are mostly out of my reach and the pigeons have to perform ungainly attempts at acrobatics to gobble them up.
This animal scarer may well work for you. It's a combined PIR sensor and water sprinkler, powered by batteries and fed by mains water connected to a standard Hozelock connector. Any warm-blooded animal moving across its range, up to 10 metres, will trigger a violent spray of water in that general direction for 5 seconds. There are limitations: Birds concealed by dense foliage are masked, which could be a problem with a tree in summer. I initially used it in an attempt to deter a heron from eating fish in my pond, but the wily bird had encountered these devices before and demonstrated that there are ways of behaving which evade detection. Fortunately, the fish learned similar skills!
THe first one I bought cost £60. After 3 years, it doesn't work as well but I still use it to protect the pond, but I just got a new one for £20, ( post free from M K Tools Ltd on eBay, batteries not included). You need an outside tap and enough hose, and to protect a tree you'd need to mount it on a pole.
Cats are quite useful, especially if you can make it easy for them to climb the tree. I once got adopted by a ferocious young stray who exterminated rats, deterred foxes and squirrels, savaged other cats and terrorised birds. I called him Ghenghis and fed him raw meat.
