The World's Longest Tree Trail (TWLTT or WLTT) is a kids's trail on Buttermilk, and is shown on the Kids Mountain Guide.  See this Aspen Times video which covers the Danny Hawks Loop, Devil's Gut, Moose Alley, and World's Longest Tree Trail:  "The Drop-In:  Buttermilk tree trails," February 26th, 2018.  https://www.youtube.com/watch?v=JgEe-2vjUXI  Photos of it, taken in April 2017, are below (click on images to enlarge).