I have 4 Maples trees in my back yard that are growing in a square. I built a large treehouse (sleeps 4) 11 feet above ground on 2x12s. Each was lag bolted on one end and resting on J brackets on the end so it could slide with the movement of the trees in high winds. A few years went by with no problems. Then one of the trees died. I cut the top of the tree off at the height of the middle of the treehouse keeping the dead tree standing to support the treehouse. After a few years we noticed that the door was hard to close. Right now it is almost impossible. The whole treehouse is now out of wack and the door frame is no longer square and plumb! Viewing the front deck of the treehouse from a distance it is obvious that the side attached to the dead tree is much lower than the other side. ( I haven't measured it but I am sure it is at least 3-4 inches difference) I also have a set of stairs attached to the side that has landing on the way up. The stairs are also no longer sitting level as the rise of the trees has pulled the steps up and pulled the landing closer to the treehouse leaving the lower set of steps tilted. I beg to differ that trees do not grow upwards!