Please help trying to identify a tree.?

I am trying to identify a tree that has taken up residence in one of my containers.It is a broadleaf.3 leaves,opposite.elliptical,but more like a slightly stretched out morning glory leaf.Dull green,not toothed with drupe type black berries,perfectly round,about the size of a pencil eraser when fully mature (went from green to black.)right now is about 3ft tall.Please help.Books only got me this far.websites no help or haven't found the right one.Also I live in San Francisco bay area.

Please help trying to identify a tree.?
You're sure it's a tree? It sounds like a nightshade, american or black. Here's a photo, just imagine the berries are black.