There is an old apple tree in my garden. It was old when I was a child. I think it is a Bramley; cooking apples, anyway.
Several years ago I cleared all the ivy that was smothering it as people told me it was no good for the tree.
There turned out to be not much actual tree left under the ivy. It's hollow, and since then more of the trunk has disintegrated, so it's just a horseshoe of bark.
The ivy has taken over again, and is probably holding it together.
Still produces apples, and this year has been ridiculous. I've given loads away to neighbours, taken two big binfuls to a local cider producer, and there are still lots at the top out of reach. Remarkable.