The “Greenest” burial is to bury in the ground a dead body unembalmed and naked. If you have to, put it in a biodegradable shroud. No coffin of any kind either. Plant a tree on the surface. The West has this weird desire to preserve and doll up a corpse for weeks and an entire parasitic industry has grown up around it to fleece emotionally vulnerable people. You can mourn the dead without the corpse being in front of you.