Uhhhh

That’s not exactly a great plan

It takes a lot of energy to produce fruit, that could be used to grow leafs and clean the air. And if you’re just doing a few small branches, the tree is going to dump resources and overproduce on that branch, risking it breaking off.

Those fruit likely won’t be eaten, except by insects and maybe rats/mice if they’re in a city.

Like, great spirit, but poorly thought out.

Way better use of time/energy to plant native flowers/clover.

Fruit tree grafting is very easy.

Take a twig cutting (a few inches long at least) cut at a thin diagonal. Line that up with a similar cut on the target plant so the bark lines up as much as possible and wrap. The bark is where the cut will heal so the branch survives.

If you get multiple varieties of apple on the same tree the tree can now self-pollinate.

It can get more complicated, you can use special ties or have a tree salve for the cut. But that’s the basics.

Anyone can do it with some practice and a little studying to make sure you’re grafting compatible fruits.