One of my childhood favorite books is Andrew Henry's Meadow.   It began my fascination with tree houses.  If you've never read it, go ahead, buy a copy and you'll understand.  It was out of print for many years, but now you're in luck.  In 2005 it was reprinted in celebration of its 40 year anniversary.
Also, I finally replaced the photo in this earlier post with a treehouse photo of my own.
