Apex domains cannot have CNAME records.
Question and response
Question
dig bme.hu. NS
Answer
bme.hu. 2 NS nic.bme.hu.
bme.hu. 2 NS ns.bme.hu.
bme.hu. 2 NS ns.thut.hu.
Authority
The response has no authority records.
Additional
ns.bme.hu. 2 A 152.66.116.1
ns.thut.hu. 4 A 79.172.212.136
nic.bme.hu. 2 A 152.66.115.1
ns.bme.hu. 2 AAAA 2001:738:2001:8001:0:0:0:2
ns.thut.hu. 4 AAAA 2a02:c647:0:ff:0:0:0:f7
nic.bme.hu. 2 AAAA 2001:738:2001:2001:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0