This Ailanthus altissima is growing in the Shakespeare Garden, otherwise known as the lower rose garden or cherry tree garden. I don't have any history on it, or anything to say why it is growing here. The common name is Tree of Heaven; an alternate common name is Tree from Hell, as it suckers and seeds itself very easily. The area around the tree has been cleaned up recently - there was a lot of sucker growth last time I paid attention to it. It can be distinguished from walnut and other trees with compound leaves by the glands on the leaf margin near the stem.