I had a massive sinkhole develop 3 years back. I filled it with rocks, gravel & soil. Last year it opened again only this time it was even larger and several feet wider underground. Turns out that when the house was built (early 70's) they buried all the trees they took down. It cost me over $2000 to have them removed & the hole filled - repairs to the rest of the yard another $300. If you can, I recommend getting out as much as possible an don't just bury it. Dependent on the tree the roots can be very deep & wide spreading