Linq OrderBy dependencies on other entities

I have collections of entities that I need to sort depending on their dependencies to each other. Here's an example because it's fairly tough to explain:

public class A {
    private B objB;
    public B propB { get{ return objB; } }
    // Some other fields and properties.
}

public class B { /* Some fields and properties. */ }

The thing is that I need to import data into collections of those types but I need to import in a certain order because if I import A objects first, I will not be able to link the corresponding B since it won't exist yet.

So what I'd like is to sort my collections in a way that all dependencies are imported in the right order (There are no circular dependencies). I can't figure out a linq statement that will do that though.

lists.OrderBy(l => l. ??? );

I was thinking maybe get a list typesList of all the types T of the List<T> in lists and somehow use reflection to count how many fields in T are in typesList but that seems... inefficient ?