Jesse was a popular image in mediaeval art; there are some beauties, including a much defaced one in St. Cuthbert's, Wells (images on line at Flickr). Damned reformation!

It seems to be a custom to make them & decorate them like Xmas trees. Never heard of this before: http://www.catholicculture.org/culture/liturgicalyear/activities/view.cfm?id=545.

Xmas trees as Trees of Life; rather than vestigial pagan rites with tinsel & baubles symbolic of the gonads and viscera of the sacrificial victims of yore. Trees of death!

Talking of which, in the Apocryphal Legend of the Rood, Christ is crucified on a cross made from the trees that grew from the dead Adam's mouth. In the Foliate Passion of Norwich Cathedral the rood is green once more as Christ is nailed to the green sins of humanity:

Foliate Passion (pic by me)