An ancient oak having grown through a church organ and afterwards whithered along with the surroundings. Brought to life with tech and psychic energy the tree now serves as a vehicle for the driver - permanently fused into the bizarre "tree instrument".
BTW, here is the initial sketch, which showed up in the corner of a bigger drawing. You might just see the outline of the man - "the composer" - worked into the tree trunk.
Fiction for the character can be found in the post on IRONSLEET.com.