Originally Posted by echinosum

Honey fungus produces fairly large toadstools in clumps and thick bootstrap-like mycelium by which it spreads. You'd see it if the tree was already dead. Armillaria - Wikipedia, the free encyclopedia It's unlikely it would kill a new fruit tree if it wasn't already in your garden killing lots of other stuff.

If the tree is just 3 years old, and died, you should be able to pull the tree up fairly easily and have a look at the roots, and see what is going on. There's one area of my garden, along a south facing wall, where I'd like to grow fruit trees, but I've tried a few times and they just die when I try. The roots never get going. I've decided it must be something in the soil, building waste or something. Maybe the tree you were given was no good. Perhaps it was potbound. Maybe there are insect pests (eg vine weevils) eating the roots. Voles seems unlikely.