You select the 2.80 branch, see below gif:
Here is the link to the 2.80 branch: https://github.com/MaximeHerpin/modular_tree/tree/blender_28
You select the 2.80 branch, see below gif:
Here is the link to the 2.80 branch: https://github.com/MaximeHerpin/modular_tree/tree/blender_28