I have a twisted /contorted / japanese/ willow tree (it is I'd say about 20ft high at the moment )next to my small garden pond. My son planted it (from a cutting) over the resting place of a deceased pet 14 or so years ago. It has grown very fast has no main trunk but four main parts, predictably perhaps, growing outwards rather than straight up. It has now been pollarded back twice. I am now wondering as the garden is small whether I ought soon to think of cutting it down and somehow stopping the root growth (chemically?) but I would prefer to retain the body of the tree in order to; a) to install a platform- balcony affair where I can sit, and b) thus to provide some shade and cover for the pond and it's inhabitants. Is this even possible?