The main advantage of trees over graphs is information density. Graphs must accommodate cycles, a requirement fulfilled by assigning a unique identifier to each node. Each edge then references two of these identifiers. Graph representations therefore incur the storage overhead of identifiers associated with both nodes and edges. In contrast, a tree can be directly encoded as a set In contrast, a bond in a molecular tree defines its target atom inline (lower right). This increases the potential efficiency of trees over graphs for molecular representation.