Juniperus virginiana. It's a very useful tree, but very invasive. Landowners of prairie grasslands will ruthlessly eradicate any start they find.
Out here we let it grow. I like the evergreen and it provides good wood for burning and building.
I love the berries and use them for winter decorating. They're prickly branches, but they smell so good!
Here's an interesting site with more information about this tree.