The tree is a fundamental data abstraction that imposes regularity on how hierarchical values are structured and manipulated.
A tree has a root value and a sequence of branches. Each branch of a tree is a tree. A tree with no branches is called a leaf. Any tree contained within a tree is called a sub-tree of that tree (such as a branch of a branch). The root value of a sub-tree of a tree is called a node (or node value) in that tree.
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