I picked this up from a tree in Greece, where the landform was plain. It is about 2.5cm (see other objects for scale). I would like ot know its name
This might be brier you're talking about.
It's hard to tell based on only that picture... it may be a type of cherry, but when I saw the post, I instantly pictured it to be a type of brier.
Looks clearly like a cherry, but might not be an edible one. The fruit is a bit ambiguous, but the leaf is a perfect match. The stem is also very telling.
A clarification on language: The sweet black cherry sold in the market is not the only fruit called "cherry". There are many types of cherry, and while I am quite sure the picture depicts one of these, I can't promise that it is a tasty, edible cherry. It is certainly not the sweet black type. It may be a chokecherry, as mentioned in the comments; botanically, this would still be a cherry, just like a cantaloupe is still a melon. Or it may be any other of a number of edible and inedible cherries.