Apex domains cannot have CNAME records.
Question and response
Question
dig ns1.bg. NS
Answer
ns1.bg. 5 NS coco.ns.cloudflare.com.
ns1.bg. 5 NS tim.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0