This morning, the Carnegie Science Center put up a a different kind of ever “green” for the holidays. A group of Alcoa employees delivered a handmade, recyclable Christmas tree made from 756 recycled soda cans to its neighbor the science center, by walking it along the North Shore trail.  The sustainable and unconventional tree was constructed by 40 Alcoa workers as a part of the company’s annual month of community service and will be displayed during the holiday season.