Make it possible to craft an apple into an apple seed, which would grow into an apple tree after you plant it (but apple trees would never be created by the map generator). An apple tree would look like a regular tree except that it would have a few leaf blocks that look like leaves with apples. The leaf & apple blocks would drop apples when destroyed, but maybe not always.
Or maybe an apple would just leave behind a seed when you eat it.
Or maybe an apple would just leave behind a seed when you eat it.
Maybe make the apple from dungeons into seeds for apple trees.