Skyrim has a dedicated tree LOD system, which uses a tree LOD texture atlas (build from tree LOD billboards) and specific data files (not true NIF meshes like terrain LOD or object LOD) to show tree LOD in the game.
While this is commonly referred to as tree LOD, it might also be referred to as standard tree LOD or traditional tree LOD when trying to distinguish between similar tree LOD with tree LOD billboards done in object LOD, e.g. ultra tree LOD.
The tree LOD billboard textures are shown on 2 double sided planes intersecting each other at a 90 degree angle.
The tree LOD system does not use normal map textures and thus has limited lighting.
The tree LOD system can only show straight up-right trees.
Tree LOD is generated if a tree LOD billboard is found for a tree in the load order. In this context trees are references that use base records of the types 'TREE' and 'STAT' with the 'Has Tree LOD' flag set.