1. An apparatus comprising: a memory configured to store at least a portion of a multi-level tree representation of an ordered multi-field rule-based classification list, the tree representation comprising at least one non-leaf level and one or more leaf levels, wherein each entry in the at least one non-leaf level comprises a count value indicating a number of rules having a matching field and entries in at least one of the one or more leaf levels comprise rule pointers arranged in priority order; and a processor configured to incrementally insert or delete rules, while preserving ordering semantics of the tree representation.