Oh I just remembered, someone who worked at an arboretum who I met a while ago mentioned that trees actually diffuse carbon dioxide directly into the soil. I think he said it was about one third of the weight of the tree? That amount would still be sequestered even if the tree wasn’t buried. But I don’t know how stable that is over the long term.
For offsets to work, they’d need to be based on the actual science of how much carbon they trap over what period of time. Different methods would need to have offset values published by the government. But I agree, offsets with algie or similar look much more feasible than trees.