If you're buying a tree that would have otherwise not been grown (such as if buying Christmas trees wasn't a thing and that land was used for something else instead), I'm not sure it's so bad though. That carbon came from the atmosphere over the last 10-15 years, so putting it back is "even" within a child's lifetime.

According to a Google search, a tree takes 7-10 years. So you were on hacker news while that carbon was in the atmosphere. Puts it into perspective

Interesting, it makes sense. Do you know what are the involved timescales here? How long before the buried wood is decomposed and has released most of its carbon back? Is it 50 years or 5000? Maybe it depends a lot on the type of soil?

EDIT: as the sibling comment observes, burning the tree cannot be "awful", as all the carbon from that tree came from the atmosphere. Growing and burning a tree is the epitome of carbon-neutral thing to do. Now, burying a tree may have a positive (non-neutral) effect.

It really depends on the local conditions. A log on the surface, in an area with things that will eat it (e.g. fungi, bacteria, termites, and other decomposers) will fairly readily give up its carbon.

If it gets covered, and spends time in a cold, anaerobic environment, there will be nothing to return it to the atmosphere. Decomposition can eventually stall out entirely, allowing it (given enough time and compression) to form coal or oil.

I'm very interested in wood gas pyrolosis, a process that pulls burnable fuel from wood and produces almost pure carbon as a byproduct. The gas could be used to generate electricity or heat, and the carbon could be buried in old mines. I suspect the economics just aren't there for it yet, (or the process doesn't scale to the numbers we'd need for large scale de-carbonization).