When creating a new world through the "Caves" option in the "Buffet" world type, no trees generate.

Steps to Recreate:

1) Navigate to the world creation menu, and select "Buffet" in the world type option.

2) Select "World Generator: Caves,' and select any biome that usually contains trees or tall plants (I tried Bamboo Jungle Hills and Birch Forest)

3) Create world

4) Observe lack of trees

5) Cry tears of sorrow for the lack of trees