Tree structure
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In telecommunication, a tree structure is a hierarchical organization in which a given node is considered to be an ancestor of all the lower level nodes to which the given node is connected.
Note 1: The root node, i.e., the base node, is an ancestor of all the other nodes.
Note 2: In a tree structure there is one and only one path from any point to any other point.
Source: from Federal Standard 1037C