A packet classification system, methods, and corresponding apparatus are provided for enabling packet classification. A processor of a security appliance coupled to a network uses a classifier table having a plurality of rules, the plurality of rules having at least one field, to build a decision tree structure including a plurality of nodes, the plurality of nodes including a subset of the plurality of rules. By identifying duplication in decision trees, the methods may produce wider, shallower trees that result in shorter search times and reduced memory requirements for storing the trees.