There are poisonous plants, but most of them can be eaten. Early summer is a good time to try out what you like, if you know what you put in yourself.
Even many of the more wild trees have edible fruits, including maple and elm. To get the best flavor, it's all about timing the plant right. You can make good pesto from the leaves or just have the plant parts in a salad. It can also be good to remove certain flowers in order to get larger fruits later.