I am trying to use data for both WTI and BRENT futures. I am using the following code to iterate between the futures contracts;however, I dont seem a way to correctly get the current symbols for both WTI and BRENT. I need to create two arrays with the closing prices of each asset, but I can only get it for one of them as of now. 

self.AddFuture(Futures.Energies.CrudeOilWTI, Resolution.Minute)
self.AddFuture("BZ", Resolution.Minute)

#in OnData
        for chain in data.FutureChains:
        #retrieving contracts from chain
            contracts = [i for i in chain.Value]

            if len(contracts) == 0:

            sortedByEXContracts = sorted(contracts, key=lambda k : k.Expiry, reverse=True)
            self.futurecontracts = sortedByEXContracts[0]
        symbol = self.futurecontracts.Symbol

        expiry = self.futurecontracts.Expiry
        df = self.History([symbol], 10, Resolution.Minute)

        df_close = df.loc[(expiry, symbol), "close"]