The tree is a term from graph theory. A tree is a set of nodes that connect from child to parent. A node can have many child nodes; each node in a tree has one parent node except for the node at the tree’s top. There are no cycles — that means at most one path connects any two nodes.
Figure 2.1 shows an example of a tree. A is at the top of the tree and has no parent node. A is the parent for B, C, and D. B is the parent for E and C is the parent for F.
There are six templates for trees. The first hardcodes an entity type for each level of the tree. The others ...
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