This uses a completely different scheme than Debian.
Let’s say I have two .crt files (pem format) for intermediate and root certs use the trust program to import them.
sudo trust anchor --store my-intermediate.crt
sudo trust anchor --store my-root.crt
It’s quite clever, it puts them into /etc/ca-certificates and renames them to match the actual name of the certificate.
sudo update-ca-trust
You can still check your certificates are imported using:
awk -v cmd='openssl x509 -noout -subject' '/BEGIN/{close(cmd)};{print | cmd}' < /etc/ssl/certs/ca-certificates.crt
References
https://wiki.archlinux.org/index.php/User:Grawity/Adding_a_trusted_CA_certificate