[otrs] Multi-level tickets classification?

Hello, I need to classify my tickets based on a multi-level tree - I actually have 3 levels, for instance: Customer / Shipment / Not delivered Customer / Shipment / Broken Customer / Payment / Invoice not received Customer / Payment / Invoice dispute Supplier / Goods reception / Quality Problem There is a total of 150+ categories. For some categories, the tree has only 2 levels. Ideally, those levels can be changed at any time during the ticket's lifecycle, but are frozen once the ticket is in any of the "closed" states. Is there a recommended method to do so? Thanks, Olivier