Pretty old apple tree in the garden which produces hundreds of not-great-tasting apples every year looks like it’s in a bit of a state. I had to cut back a weird branch that had been cut before, presumably because it shot out horizontally, and there’s a ton of rot.
It’s not in danger of hitting any buildings if it ever does fall, although could maybe take out a distracted child or two if I’m lucky.
Is there anything I can do to save it?
I'll take a guess at the second! If the tree is planted too deep (with the bit where the trunk flares out under the soil level) then it'll be constrained/ might rot.
I wonder if the mulch volcano is over-mulching?
Ok! That's super helpful. Your explanation also makes sense for them both being flavors of the same thing (apparently it's important that the flare is exposed to open air)