I think you could say part of one’s identity exists outside of the person. Their self-identity should be respected and often will align with what they project outwards, but that’s where people get confused about a person and then stubborn ones get fed up with the whole idea.

Anyway, in this case since the tree lacks sentience, it wouldn’t have an internalized gender that we could know, but we can see that its sexual characteristics have changed and give it a transexual label. The trans label can cover both.