On the latest version, and also the previous version, the exclusive roots option in the category.json does not seem to work.
You are able to loop around to a locked root and unlock it. I assume this is not intended.

Screenshot of the issue using the default 'combat' tree:

This is intended behavior.

The wiki seems to imply otherwise?

Or I suppose this just means you can't start from another root skill.
I understand now, sorry.

I think it would make more sense for other roots to not be unlockable once one has been picked. But maybe that's just me.