Mer

Just wondering if an ETF contains another ETF as it's only holding is your mer the combination of the two or just the mer of the one ETF containing the other. For example vfv primary holding is voo ... So how is the mer calculated and does voo mer and vfv mer both drag down your return or is the mer for voo set to zero and you pay the mer of vfv. Is it better to have an ETF that directly holds its stocks instead of another fund which then holds the stock ?