Compare Lists with custom objects, which have a common superclass

I have a Metamodel that's built like this:

class ModelElement
 {
     string id;
 }
 
 class Package : ModelElement
 {
      List<Package> nestedPackages;
      List<Class> ownedClasses;
 }
 
 class Class : ModelElement
 {
 }
 

Now I've built two Models and I want to check if they're identical. I'd like to compare the ID's of the Elements and I don't want to write a method for any type of Element.

Package a; //pretend both have classes
 Package b; //and nested packages
 compare(a.nestedPackages, b.nestedPackages);
 compare(a.ownedClasses; b.OwnedClasses);
 

Since Class and Package both inherit from ModelElement, both have IDs. So I want to write a Function "compare" which compares the IDs. I thought of using Generics but the generic datatype doesn't have the attribute "id". Any ideas?

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