This is a bog birch, Betula verrucosa. They grow in wet areas all around northern Europe. I found this tree in a bog very close to my home abut 15 years ago. After many years in the growing bed I planted it into a container about four years ago. From then on it was the ugly duckling, too large to ignore, but not good enough to put onto the shelves. Today I found that it now is good enough for the gallery.
80 cm high, about 50 years old, pot by Petra Tomlinson.