[@Disciple Cain]

Thank you so much for this ^^
I'll go with some 'wood elemental' types from other games.  Stick man > Wood walker > Treant > Revenants > Treelords or something like that.

He was a normal player, but I have an idea where he started following a druid progression line and just kind of got sucked into the story and where it was going.  Maybe there was a secret conclave of druids that worked to keep things in balance and he played the game in pursuit of their storyline and faction achievements since he got roped into the story of Yggdrasil and liked the kind of guardian of nature character he was making.  It didn't hurt that he himself was an avid outdoors man, scientist, lover of science with an animal lover girl friend.

Think World of Warcraft's Cenarian Circle, a kind of faction that was only available to the Druid Class to join and take their quests.

The original concept of him is that he likes to help people so intentionally chose a class that can essentially fit roles for the parties when they need it, kind of favoring versatility over specialization with the balance of the game making it a viable option that would allow him welcomed to pick up groups often.  There's other factors that he likes to stand out and picks unusual and generally odd ball things to get unique experiences.  He loved the idea of being a kobold > lizardman > Naga > Dragonoid but being a walking tree was just too weird to pass up.  (He also considered a slime too)