This stuff really varies and can be rules from insurance, your particular plan or even the pharmacy benefit manager (PBM). I have Aetna and it covers Lantus but considers Novolog as a branded non-preferred medication.
Aetna covers Tresiba, perhaps you could try a sample of Tresiba? Also you might find that your insurance covers the new Basaglar which is the biosimilar for Lantus. At least one PBM announced they were not covering Lantus and instead were steering patients to Basaglar.