Artist Prof. Sam Van Aken took this to the logical extreme with the Trees of 40 Fruit https://en.wikipedia.org/wiki/Tree_of_40_Fruit
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.
https://raintreenursery.com/products/fruit-cocktail-4-varieties
$120 for a tree that can grow 4 separate fruits
I don’t know I feel like half the fun would be seeing if you could do it yourself, then again some people just would like to own one I suppose