You can dig holes in the ground and plant apples in those holes that grow into apple trees. Any place that you can dig a hole for a pine tree could also be used for a hole for an apple tree. I like to keep my apple trees in an area that is a bit away from the pine trees.
Also, since you can build bots that hit pine trees with mallets to get sticks, you can build bots that hit apple trees with mallets to get apples, so I like to keep the apple trees in one group and the pine trees in another group.