// input

customer
  item
     producer
     "Novartis"
     "Basel"
   "xyz1"
  "Huber"
  "Basel"
customer
  item
     producer
     "Novartis"
     "Basel"
   "xyz2"
  "Huber"
  "Geneva"
customer
  item
    producer
      "Novartis"
      "Basel"
  "xyz3"
  item
    producer
      "NovartisB"
      "Basel"
  "xyz4"
"HuberB"
"Basel"