The Problem

        $> cat automobiles_taxonomy.csv

        path,audience_size,cpm,buyable
        "|General Motors","","",0
        "|General Motors|Chevrolet",1000000,0.80,1
        "|General Motors|Chevrolet|Spark",100000,0.15,1
        "|General Motors|Chevrolet|Sonic",150000,0.20,1
        "|General Motors|Chevrolet|Cruze",250000,0.20,1
        "|General Motors|Chevrolet|Malibu",200000,0.25,1
        "|General Motors|Chevrolet|Impala",175000,0.30,1
        "|General Motors|Cadillac",150000,1.00,1
        "|General Motors|Cadillac|Coupe",150000,0.30,1
        "|General Motors|Cadillac|Sedan",150000,0.35,1
        "|General Motors|Cadillac|Crossover",150000,0.40,1
        "|General Motors|Cadillac|Escalade",150000,0.50,1
        "|Toyota","","",0
        "|Toyota|Corolla",800000,0.60,1
        "|Toyota|Camry",600000,0.70,1
        "|Toyota|Prius",400000,0.80,1
        "|Toyota|RAV4",300000,0.50,1