The set of linked node with one node as a root making an acyclic, connected graph is said to be tree in Computer Science. When one tree have unique path from node to any other node then that tree is said to be acyclic. The figure below shows how a tree would look like.
A tree with hierarchy. Source:Wikipedia
The common use of tree is to represent data in hierarchical manner such that the storing and searching could be easier in future. It helps in representation of shorted list of data. In visual effects it can be used as a workflow for composition of digital images. Moreover, it is the foundation for different algorithms such as Routing algorithms.