Add a new structure/dungeon without messing too much with the world generation

Hi 🙂 I think the title is self-explanatory. I want to add a new structure that should spawn on the surface in forests / plains (it's a big tree with a custom mob I made inside it) Any idea on how to make it without messing too much with world generation? My datapack is not meant to add the dungeon but the mob itself is the real feature, I do not want my pack to be a problem for world-generation-meant packs.