I say it's hickory.  Pignut (or Mockernut maybe?).  That sapling would make a Great bendy handle bow!!  Cherokee style flatbow, or maybe something like a Sudbury where the handle is rigid but not too high.  
For those suggesting Pecan: Pecan is not very common that far north (Pennsylvania right?), and its compound leaves have many more leaflets (To me it looks kinda like a wimpy Black Walnut leaf, they're both usually much longer and have more leaflets than hickories).  Also the bark on pecan is usually rougher looking from what I remember living in Tallahassee and Quincy, FL, where it was/is very commonly planted in rural areas.