The WoodTypeBuilder#build method mentions using the WoodType.register method:

However, the access widener for this method is not transitive, meaning it is private to API consumers:

Note that the test mod uses this method, so the test mod currently does not provide a working example of using this API:

What would happen to the build method then?

The WoodTypeBuilder#build method could be kept if the access widener is made transitive. I would imagine that solution would be preferred over leaving WoodTypeBuilder#build useless and updating the documentation accordingly.