Conditional proxy_pass based on current location

Question

I want to do this

location ~ /.*$ {
    proxy_pass http://mysecondapp.local;
}

but only if the user is in /mysecondapp or in /mysecondapp/something and not the root url or anything else.

This is the configuration for /mysecondapp:

location /mysecondapp {
    proxy_pass http://mysecondapp.local;
}

How can I do that?

I tried to put the first location inside the second one, but that didn't do the trick.

Thank you for the help!