https://www.backtrader.com/docu/dataautoref/#genericcsvdata

You have to indicate the position in which column each field is and which fields are not present (with -1)

In your loading example not a single column is specified and the code tries to find the values in the default column ordering (datetime, OHLCV)

In any case, your data is NOT tick data. Your data is bid/ask, which isn't the same. You have to choose in which fields you want to load the data.