Spirits living in trees is a pagan idea, found in many places in the world. The "Jack-in-the-green" concept is found not only in England, but etchings and prints of a tree spirit "Jack-in-the-green" have been found in Germany, as well. Examine the Gustave Doré etching above (intended for Dante's masterpiece). Again, one finds the influence of the pagan idea of a tree spirit.