If this concerns older saves, then those could be Growfruit trees? They spawned during the challenge back in 2016 and replaced some of the other fruit trees. Obviously that was a while ago. I still have them in parks and other areas with wild growing trees in my older saves. In my newer saves I just add them by placing a room I have saved to my library. They make for good fertilizer.
Edited for picture:
https://i.imgur.com/pU2Bcd8.jpg