I'll add you later today, Gariputo. Once I plant the pears and persimmons I just got from a friend I'll have every fruit available for trade.
Apples are my native fruit. And there's not much reason to sell them past the first few days of the game, but there are a few good reasons to grow them. One is for trading purposes; another is as a low-cost option to test where trees will successfully grow -- if a tree successfully grows in a spot, ANY tree will grow there, so I'll eventually chop down most of my apple trees and replace them with lucrative non-native fruit. It's probably overly cautious, but I hate taking a chance on planting a non-native fruit in an untested spot and just having it die immediately.
Also, only your native fruit can grow "perfect" versions, which sell for big bucks in other people's towns (assuming they don't have the same native fruit as you). Using the method described above, you can chop down a native fruit tree and replace it with a perfect version, which will always sprout 3 perfect fruits each harvest. Downside is perfect trees die after several harvests, but as long as you hold on to one perfect fruit per tree you can always just replant it.
Lastly, if you care about getting a "perfect town" rating, you need 110-200 trees in your town (among other requirements), so I've been planting a crapload of apple trees for the time being to try to reach that milestone sooner.