Hi presj and Welcome to the Forums! You got a Mushroom Tree stump! Those are super cool and will turn into a giant mushroom in the Spring. You can pop a Tapper on them and get mushrooms from it if you want. Keep it there until Spring just in case you like how they look. I love 'em!
Mushroom tree stump, I believe. Trees have a very small chance of turning into mushroom trees during fall, and mushroom trees turn into stumps over winter. It'll grow back in spring if you want to keep it.