Luc.
do u ever bust up the leaves and smell them?
this is a good way to dentify unknown plants.
It's like a taste test with your nose. You can detect odors that are tell tale for certain families of fruit.
be careful though, some leaves can stain your fingers (i think black sapote), and some will burn your face or skin.
But if you crush leaves and smell them, you'll find it's one of the best clues for identifying a plant. Make sure to smell the leaves of a fruit you might suspect your unknown fruit is akin to...this way you can compare the smells for similarities.
Best of luck, Luc.