Apex domains cannot have CNAME records.
Question and response
Question
dig tetra.in. NS
Answer
tetra.in. 5 NS ns37.domaincontrol.com.
tetra.in. 5 NS ns38.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0