Apex domains cannot have CNAME records.
Question and response
Question
dig expertus.com. NS
Answer
expertus.com. 5 NS ns-2028.awsdns-61.co.uk.
expertus.com. 5 NS ns-232.awsdns-29.com.
expertus.com. 5 NS ns-649.awsdns-17.net.
expertus.com. 5 NS ns-1192.awsdns-21.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0