secure-reverse-ssh-tunnel/config

Host jumpserver
     Hostname <IP>
     User root
     IdentityFile /home/<USER>/.ssh/<ID>

Host HostToExpose
     Hostname localhost
     User <REMOTE_USER>
     Port 20001
     IdentityFile /home/<USER>/.ssh/<ID>
     Proxycommand ssh -W %h:%p jumpserver