A Quality Management System is often represented as a pyramid. Which is a relevant analogy. It has some “depth”, it is not a flat structure, and it matches well the hierarchical nature of many human thinking processes, of organisational structures, and of many information system paradigms (e.g. folders/subfolders). Consultants and other experts who use this analogy typically describe from 3 to 6 levels. All these options are valid. A QMS does not have - by essence - 3 or 4 or 5 or 6 levels.