I don't think it is anything unusual ... but I'm not too good at trees! It is growing wild beside a footpath at the edge of woodland in South Yorkshire, UK
it's a ( Betula )
A Birch tree, of which there are many varieties, exactly which one this is, I'm not sure.
For more help see: http://www.hort.uconn.edu/plants/keys/trees/Birchkey.htm
sorry but this isn't a Betula, it's an Alnus. Still in Betulaceae, but the cones (immature pic 1 and mature just visible in centre bottom of pic 2) distinguish between the genera. I would say it is probably Alnus cordata from the shape of the leaf base and toothing on the leaf edge.