Trees are a sub-type of the more general node-edge graph data structure.

To be a tree, a graph must satisfy two requirements:

The tree data structure is quite common within computer science. Trees are used to model many different algorithmic data structures, such as ordinary binary trees, red-black trees, B-trees, AB-trees, 23-trees, Heap, and tries.

it is common to refer to a Tree as a Rooted Tree by:

choosing 1 cell to be called `Root`
painting the `Root` at the top
creating lower layer for each cell in the graph depending on their distance from the root -the bigger the distance, the lower the cells (example above)

common symbol for trees: T