I want to add a new address to the following document

{
    username: abcd,
    password: xyz,
    addressList: {
        key1: {
            addressLine1: "12th Street",
            addressLine2: "Park Road",
            City: "Kent"
        },
        key2: {
            addressLine1: "12th Street",
            addressLine2: "Park Road",
            City: "Kent"
        }
    }
}

Can I add a new address without specifying the key and let MongoDB generate a unique one itself?