Apex domains cannot have CNAME records.
Question and response
Question
dig bg. NS
Answer
bg. 5 NS d.nic.bg.
bg. 5 NS p.nic.bg.
bg. 5 NS b.nic.bg.
bg. 5 NS a.nic.bg.
bg. 5 NS c.nic.bg.
bg. 5 NS e.nic.bg.
Authority
The response has no authority records.
Additional
a.nic.bg. 144464 A 192.92.129.99
b.nic.bg. 155847 A 193.68.3.232
c.nic.bg. 144865 A 193.68.99.99
d.nic.bg. 164343 A 194.0.32.1
e.nic.bg. 144464 A 185.143.80.1
p.nic.bg. 144464 A 204.61.216.110
a.nic.bg. 144464 AAAA 2a02:6a80:0:0:192:92:129:99
b.nic.bg. 155847 AAAA 2a02:6a80:0:0:193:68:3:232
c.nic.bg. 144865 AAAA 2a02:6a80:0:0:193:68:99:99
d.nic.bg. 164343 AAAA 2001:678:3c:0:0:0:0:1
e.nic.bg. 144464 AAAA 2a02:6a80:530e:0:0:0:0:1
p.nic.bg. 144464 AAAA 2001:500:14:6110:ad:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0