Need help identifying a fruiting tree similar to blackberries to rule out if poisonous?

My parents have a fruiting tree that sprouted to quite a large tree out of nowhere. It's bearing fruits right now that are similar to blackberries, actually almost exactly like blackberries. Had I not noticed it was on a tree instead of a bush we might have accidentally confused the two as they are both in season right now in PA. After examining the tree, it was tall. Close to 20 feet. Its branches were long and spindly hanging down as it was bearing lots of fruit. There seemed to be no "prickers" or thorns on the trunk or branches. The branches almost seemed to intertwine/wind around neighboring trees. When searching images myself online it seemed to be either a boysenberry or mulberry tree. It looks more like a mulberry in my opinion because it is thorn-less. I'm intrigued being a wine-maker and jelly maker to see if these are edible. Are there any fruiting trees that bear fruits that resemble blackberries that are poisonous in case it is neither a mulberry or boysenberry tree? Without further knowledge it's not a risk I would want to take unless I knew for sure. Thanks in advance!