If I understand the use case correctly, you would like to get the general classes based on sub-categories from another model.
If that’s the case, wouldn’t a simple mapping just work, i.e. check for the predicted class and apply a mapping to get the more general class (tree, flower)?
I can imagine the opposite use case might work with a staged model, but I’m not sure if a simple if-condition couldn’t work “perfectly” here.
Let me know, if I misunderstood your use case.