"Which Laburnum it is I'm not sure. There are two wild species, native to the mountains of southern Europe, L. anagyroides (Common Laburnum) and L. alpinum (Alpine Laburnum). Most often cultivated is a hybrid of the two, which has the most extravagant flower clusters. Note the pea-flowers. Yes, it is a legume. A leguminous tree, but beware of the peas. They are poisonous..."
And now, the dangerous peas: