The Treehouse is a generated structure in the Ruins mod.
The Treehouse is a multi-level structure with a hollow trunk. Inside the tree's hollow trunk is a chest embedded beneath a gravel pillar with ladders attached, and a tank of glass blocks on the ceiling containing a lava source. If a careless player attempts to dig out the gravel to get at the chest, the rest of the gravel will collapse and the ladders will break, allowing the lava to flow freely and (consequently) set the tree on fire.
Disarming the trap is simple: Climb up the ladder with an empty bucket in hand and extract the lava, or cork/erase it with another block. This allows the player to examine the chest contents safely and, if desired, rebuild the ladder and secure the structure.
As a Shelter Edit
Much of the reward is in securing the treehouse itself. The chest contents are mostly common and usually not worth the effort (possibly to punish the player for their greed). However, with a little work, the tree itself can be secured for a quick shelter. Eight large chests- use Reinforced Chests for higher capacity- can be stacked on the opposing walls of the trunk. The glass ceiling can be hollowed out to make an Enchanting Room with space for 22 bookshelves. And the first Upper Floor is large enough for whatever living space one can think of. Plus, the various levels of the tree provide good vantage points for sniping distant players or mobs. If you're looking to build a treehouse, this is one of the best ways to get one with minimal effort.
Video Link Edit
Video by PopularMMOs