Traefik file routing match a specific subdomain to all top level domains

I have multiple top-level domains like "example.com" "example.at" which all have the same subdomain "staging" I now need to point all domains "staging.example.com", "staging.example.at" to one specific docker container. For readability reasons, I am doing this inside a file provider.

What I already had was a Rule for each domain, but is there a simpler solution with wildcards that I can use?

Old method I had

rule: >-
(Host(staging.example.at) ||
Host(staging.example.de) ||
Host(staging.example.nl) ||
Host(staging.example.uk) ||
Host(staging.example.ch) ||
Host(staging.example.eu))

New method which does not work

rule: "HostRegexp(staging.*)"