There is a Jack Vance story called "Son of the Tree" The spoiler is that the bad guy becomes a tree (he planned the destruction of many) and in so becoming (a tree) he ends up as a good guy - but (ha!) very much changed in appearance and attitude.
I think this illustration would by far suit the cover of said book; much more so than the cover on the copy I have, or even any of the alternatives.
It's a great painting and has a dark morose overtone that would fit well with the inflection implied in the story. Well done.