I have a multi stemmed tree perhaps 15ft (5m) tall and about as wide. This year it has large numbers of small fruit. The fruit was Green, then reddish, but ripens dark blue or maybe black and has a black seed that could be mistaken for watermelon. Flesh is sweet with an unusual flavor. (Sampled and spit because I have no idea what it is.) Pictures attached.
I think I have a nannyberry based on the info from that other thread. Will verify details of the tree in person soon. Discovering a large established food plant is awesome!