Here is a common sight in poison ivy country, which is much of the United States, east of the Rocky Mountains.
Poison ivy loves to climb. Here it has climbed a tree, with layer and layers of poison ivy vines on top of each other.
While it climbs upwards, it also sends branches out sideways to gather light. Often people mistake these horizontal branches for tree branches and break them off for kindling or other uses. Breaking poison ivy vines will always release lots of sap containing urushiol, the oil that causes the awful rashes.