The only graphic type that's mandatory is the Mature type! Anything else is optional:


Any given texture should be pathed as followed:
[Mod Root Folder]\Textures\BetterTrees\[TextureName]\[GraphicType]\[TextureName]_[GraphicType][RandomIndex].png

[RandomIndex] = Letter starting from A (all the way to Z), for each alternate texture that can be randomly selected by the game.

Example path:
MyTreeMod\Textures\BetterTrees\MyOakTexture\Mature\MyOakTexture_MatureA.png