Notes
How to build a chained SSL certificate
$ cat domain_name.crt domain_name.ca-bundle > domain_name_tree.crt
or, in case of a set of separate COMODO certificates:
$ cat domain_name.crt COMODORSADomainValidationSecureServerCA.crt \
COMODORSAAddTrustCA.crt > domain_name_tree.crt