At the time coal deposits formed the bacteria that broke down lingin and cellulose hadn't yet evolved, so just burying trees wouldn't work today as they would decay. You could probably burn the wood to produce charcoal (burning it in a low oxygen environment), and the bury that, but just cutting down a forest and burying it won't work.

In a low oxygen, low water environment it would work fine.

For example an old coal mine and then seal it.

Old coal mines are too dangerous for humans to enter so you need some kind of robotics to load them up with trees and other biomatter to bury.

This would never scale.

I'm no chemist, but, wild guess, you might actually make things worse by favoring decomposition into methane instead of CO2.

I would think that a proper solution would require figuring out how to get all that carbon into a chemical form that is chemically stable and won't biodegrade. The ideal looks a whole lot like coal, I'd guess?

Yep methane is multiple times more potent as a greenhouse gas.

You also need to find a way to speed up tree growth rate by 10x or 100x for this solution to be effective before most of the damage is done.

My understanding is that when wood first appeared on Earth nothing was able to decompose all of that cellulose for millions of years until microbes evolved a way to break the molecules apart and feed on them. I don't know if simply burying the trees is enough to sequester it away now that wood decomposes so readily.