fromList
  [ ( fromList [ "a" ]
    , fromList
        [ Transaction
            { transactionData = ()
            , transactionItems = fromList [ "a" , "b" ]
            }
        ]
    )
  , ( fromList [ "a" , "b" ]
    , fromList
        [ Transaction
            { transactionData = ()
            , transactionItems = fromList [ "a" , "b" ]
            }
        ]
    )
  , ( fromList [ "b" ]
    , fromList
        [ Transaction
            { transactionData = ()
            , transactionItems = fromList [ "a" , "b" ]
            }
        ]
    )
  ]