A computing system accesses one or more code lists, each including a plurality of items, each item comprising an alphanumerical machine code mapped to a human recognizable concept. The system may receive a query from a user, determine any matching and/or related items in the code lists, and generate an interactive visualization of the matching items. The visualization allows the user to view and detect relationships between items from multiple code lists in a manner that is not possible through review of the lists separately. The user can select nodes in a tree structured visualization to initiate addition of the corresponding alphanumerical machine codes to a custom code list.