I noticed today that the top two courses of bricks in my backyard wall were separating. When I looked at my neighbour's side of the wall I discovered that there was a small tree growing out of the side of the wall. I'd been aware of the tree there because it was well above the height of the wall but I assumed it was growing out of the ground! My neighbour works away for months at a time and has now been away since February, so I climbed into his back and sawed the tree off about 3 cm from the wall. But I don't want it to grow back so I was hoping that someone could recommend something to kill the root. Thanks.