Wilderness is a datapack that focuses on adding small decorations to biomes, usually on the surface with bushes, flowers and ferns, but also in rivers, oceans and even the nether. Other than trees, most vanilla forest biomes don't have many decorations in them. In Wilderness, biomes like forests look overgrown and feel much more wild. Wilderness still stays true to vanilla by only using logical natural blocks (no stone buttons for pebbles).
This pack uses an addition system that allows for extended compatibilty when used in vanilla, but it also has extra compatibiliy with Lithostitched. Whenever convenient, I recommend installing Lithostitched, for increased performance and more thorough world generation.
Wilderness does not change tree generation. For improved trees, check out Better Trees. Some of the images were taken with Better Trees.