Biomes are read from JSON files in the biomes subfolders of behavior packs. Loading enforces one biome per file; the file name and the actual biome name must match. Adding a file with a new name to the biome data location will make it available for the game to use, while existing biomes can be overriden via files that match their existing name. Note that if you add a new biome you'll need to write component data that allows it to participate in world generation (see full schema below), or else it won't show up in your worlds!