Apex domains cannot have CNAME records.
Question and response
Question
dig odessa.ua. NS
Answer
odessa.ua. 5 NS sx.ns.ua.
odessa.ua. 5 NS ns.od.ua.
odessa.ua. 5 NS nix.ns.ua.
odessa.ua. 5 NS ho1.ns.od.ua.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0