Lunar Mushtress on the Lunar Island?

[CakeyLover]

Hello. I'm trying to make a mod about expanding the Lunar Island. And I want to start by adding Lunar Mushtrees and Mush Gnomes to the biomes of the Lunar Island. But I don't know how. I already have the base of the mod, with Modinfo and Modmain.

All I want to do is add an already existing structure and mob to an already existing biome.

An example of what I need is the image that this Topic has. (I made it by spawning stuff with the debug menu)