Seen in Cambridge, MA. A quite large tree. The birds were going crazy eating these fruits that look a bit like tiny cherries (about 1/4" or 6mm in diameter). The pits in the fruit look like very small cherry pits. Photos are attached of fruits and pits on the ground. I couldn't get close enough to the foliage to get a close-up of a leaf. Thank you.
Berry looks like a Choke cherry to me but tree is rather large..
The leaves in the first pic look more like Black Cherry Prunus serotina
Resin, I think that is what it is. I should have taken a picture of the bark to post, but I think you have got it correct. Thank you. Paul