Frankentrees

Artist Prof. Sam Van Aken took this to the logical extreme with the Trees of 40 Fruit https://en.wikipedia.org/wiki/Treeof40Fruit

Fruit tree grafting is extremely easy. You can graft a twig from several apple varieties into one tree, letting that one tree self-pollinate.

Editing to elaborate a little:

Cut the twig at an angle, leaving as much cross section of exposed bark as possible. Then line it up with a cut branch on the tree so the cut bark joins up - if it can't heal it won't take. Then tape it up. I had a special kind of tape for the class but I don't think it matters so much as long as you can keep them joined.