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In this part, you will learn how to summarize trees in terms of their component splits. A
Split class will store the set of leaves that descend from a given node. A tree topology can be identified by the set of splits it contains. A tree ID is thus a set of splits in a tree, and all trees with identical tree IDs have identical topologies. By the end of this section, your program will read a tree file and report all unique tree topologies and the number of trees having each topology.