At the climax of the episode Lief's Destiny (Part 2), the crystalline tree-castle is created from the mysterious chest that sprouted at the base of the Tree of Teamwork in Prince Komodo (Part 2). The chest is launched from the tree to a site on one side of Hub City where, in a matter of seconds, the tree grows into its full size.
The tree-castle bears some resemblance to the small castle, at least the aboveground portion of which is destroyed earlier in the episode by Dr. Maniac, but is many times larger and appears to have a multi-level castle in its branches, which includes great three balconies, spires, and towers. The castle is decorated iwth aqua colored diamonds and above the doors are Princesses Marillia and Marina's heart and star symbols. The structure has at least one banner flying on the side marked with the Hub logo, and diamonds. Two sets of seventeen strings of beads hang off the side of the structure much like the beads that hang off the Friendship Rainbow Kingdom castle. At the foot is a great golden stair for the two-leaved golden door into the tree's body. Two open lancet windows flank the door.
The lobby's two stairs lead into the hundred and twenty castle rooms where lancet two-toned aqua glass windows and white quartz crystalline lathed columns with scrolled tops line the hall decked by a brown rug with scrollwork. At its end is a golden-framed aqua glass fanlighted door to the throne room where the Hub Squad and Jasmine and Barda each have a crystalline throne about a star-shaped dais on a golden dish on a red rug with scrollwork. Even with its door are a set of green glass spire lights.
Beginning with the season premiere, the castle takes the small castle's place in the theme song.
In Hub Map (Part 1), the castle reacts to the Hub Squad's teamwork symbols, and a crystal platform rises from the center of the throne room and creates fifteen bracelets for each Hub Squad member and a three-dimensional interactive map of Hub Island. The map calls the Hub Squad to a remote village to solve a teamwork and friendship problem.
In Castle Is Where The Heart Is, the castle is shown to contain high-rising ceilings, glass stained windows which hold the memories of Lief's quest to save Deltora, statues of his friends from Hub City and Deltora, long hallways, and a dining hall that Lief and his friends hold a pancake and waffle breakfast in. To make the castle feel more like a home to Lief, his friends fashion a gem-lined chandelier from the oak tree's roots and hang it in the throne room. In addition, Strawberry decorates the dining hall and spruces up the kitchen with "berry fancy utensils and cookbooks," Twilight puts new books in the shelves and posters on the walls in the library, Dennis, Guy, and Wakko places some toys, a skateboard, prank stuff, video games, and SheZow stuff in Lief's bedroom, Buster, Yawp, Dander, and Lucky have put up superhero posters on the walls and installs a number of toys and pet beds in the playroom, Betty has put exercise equipment in the workout room, Komodo and Robbie have put tool decor, computer, and gadgets in an empty room in the first floor that has now become a technology room, Trafalgar and Sabrina have put wands, spellbooks, charms, potions, and the cauldron in another empty room in the fourth tower that has now become a sorcery room, and Blythe brightens up the guest room with fabric, fancy patterns, posters, pet stuff, and her mannequins with her pet fashions. There are also signs that are hung up on the doors so that way, Lief will know which room is the right one for him to go to.
The castle also makes another appearance in Discord's Birthday Surprise!.
In Sugar Rush!, it made it's second appearance when Lief was exercising in the workout room.
In Zombie Gas!, Lief mentions that there is a treehouse in the Royal Gardens.