It was impossible to identified until it flowered. Seems a cherry or any other prunus.
Rhamnus cathartica bark.
Rhamnus cathartica seedlings
The shiny black berries of this rather invasive plant
European Buckthorn (Rhamnus cathartica)
berries (as of July), leaves, and terminal pseudo-thorn.
I found one patch of Common Buckthorn in se PA unfortunately
Foliage and fruit in ne IL in August 2014