Carl the Collector Episode 13 The Autograph Collection/The Rope Collection >Sheldon obtains left-over wood from his father and decides to build a tree fort with Carl in Carl's backyard, inviting their friends over to help. Carl disregards his friends' attempts at planning and collaboration in favor of building the tree fort exactly how he envisions it. In response, his friends decide to build their own fort on a nearby tree without Carl. After the tree forts are finished, with Carl's being an enclosed structure with a window and the others' being a fenced platform, Carl realizes he forgot to include a door, trapping him inside. After recovering from a panic attack, Carl uses a whistle to alert his friends and uses a makeshift rope ladder to escape, with his friends providing pillows to cushion his fall. Carl realizes he excluded himself from the team out of close-mindedness and that his friends' tree fort was better than his. Nonetheless, Carl and the friends decide to connect the two tree forts using a rope bridge.