Take a picture of the whole tree. Take a picture (more closely, with your hand in it) of where the leaves are attached to the stem.
Near as I can tell from these images, the plant looks like it has opposite arrangement of simple leaves, with some big fat terminal buds. The bark on the younger trunk and branches reminds of cherry bark. This leads me to believe that this could be a Syringa reticulata - Japanese Tree Lilac.
Might be odd to consider, but it could have been planted before you got there. You haven't given us information on history of this site.
