How do we know when it's a tree and not just one of its fruits? I said just "plum" and it was wrong
Is there a given rule about that? I've had this problem before. If it ends in ă is it just the fruit?
Generally yes: prun 'plum tree', prună 'plum'; cireș 'cherry tree', cireașă 'cherry'; migdal 'almond tree', migdală 'almond'; piersic 'peach tree', piersică 'peach'. The name of the tree is masculine; that name of the fruit is feminine.