Do not, i repeat do not tie yourself to a tree. If that tree is willing to make the ultimate sacrifice, let it go. Instead encourage the planting of newer seedlings in its place. Falling rotten tree branches are an unnecessary occurence in the parks and byways of America. Next year on Memorial Day plant a rogue seedling in its place if the city doesn't do it for you. Just let the old tree die...and move on
Just to update everyone who took an interest, this is what happened: There was interest from the local media, and even 30 seconds on the local TV news, followed by a couple of heated public meetings. The developers looked suitably sheepish, but brought out their tree expert who insisted that most of the trees were actually unsafe, and liable to topple at any minute. He even said that one of the trees was flawed because its trunk forked, instead of going straight up and down! Anyway voices were raised, and after much moaning and groaning they decided to save half the trees that they had planned to fell. So the protest wasn't a total success, but it was worth doing.
Well done. Not only have you saved some of the trees you've also shown that the locals do care about their community and put the council on notice!