>> reporter: the man behind the tree's 40,000+ lights is david gigerich. >> i actually bought scaffolding to put the lights on. i have to use a boom lift to get the star on the top. and quite frankly, i spend three weeks putting the lights on this tree. it's the most exhausting yet exhilarating time for me. >> reporter: there's a good reason for that. david doesn't feel alone when he's decorating. he feels like his son duncan is right there with him. >> the best part of duncan-- and everybody who would ever talk about him would say, his warm heart, his warm smile, and his big laugh. >> reporter: three years ago, duncan's life was cut short when he was in a car accident. he was just 19 years old. for david, the grief was almost unbearable, especially during the holidays. as a way to honor duncan's life, the neighborhood bought his family a memorial tree. >> and we went to a tree farm, literally walked over a hill, and it was the "ta da" moment. there was the tree. >> reporter: and over the past couple of years, it has doubled in size, from 15 to 30 feet. that means more lights, more work, which david is just fine