Is your apple tree large HC? In a pot or small in the ground? How old? How dry? Has it been fed recently or allowed to dry out completely? Ants like the sweet stuff that aphids let out. Suggest a good soaking if in a pot. Put the hose there to trickle at the base if in the ground. Wait and feed too. The ants probably don't do any harm if a large tree. They might bite you more than the tree!!!

Put a grease band round the trunk. As Dorjac says, water and feed.

I grease banded my 10 trees and supports in my mini border orchard Dr Bob.....what a messy job!!! The ants are still wandering around Discovery in spite of. I think they are wandering over the corpses of their comrades who bravely went before. I went to summer prune Discovery, as it is early. I am still itching from the ant bites on my hands.