Like most other people, my husband and I are obsessed with Halloween lawn decorations. We enjoy skeletons crawling up walls, spiders on cloth webs, blow-up cats with moving heads, skulls mounted on spikes. We were thinking of trees as mere launchpads; a tree is a spot where you stick a spooky owl or a bat-with-fangs. But a couple of houses in my particular neighborhood have recognized that a tree itself can be so much more. The tree can be the source of fright--the tree, on its own. One 3-D inflatable takes the form of a black tree with green eyes and a green mouth. At another house, a kind of mask has been mounted onto the tree, so it seems as if there is a face growing out of the bark. This leads me to think of one of my favorite directors, Tim Burton, who has regularly made use of trees in his work. Famously, there is the Tree of Death, in "Sleepy Hollow"; I can never follow the plot of this movie, but the tree in question seems to be a gateway to Hell. (The trunk is ...