What are the advantages of eating apples?

Each apple gives you 16 health, and makes a nice crunchy minecraft eating sound

Thanks. You could provide this information on the informtion page :-)

Do all trees generate apples or you added an apple tree? or do they suddenly materialized like a dropped item on the floor that you pick up?

The apples are dropped like wood when you chop down the tree. The drop rate is loosely based on the overall growth and health of the tree, so dead trees without any green leaves will not drop any apples, while trees with more green leaves will drop more apples