Calling a generic method with the correct derived type

I have the following scenario:

I have three classes, let's call them A, B and C. All they have in common is that they inherit from the same interface, ISomeInterface and that they are classes that are mapped to entities using Entity Framework.

I have a method that received a List of objects that implements this interface, but the objects themselves will be instances of A, B or C.

The method shell looks like this

public void MyMethod(List<ISomeInterface> entityList)
{
  foreach(var entity in entityList)
  {
    ProcessEntity(entity);
  }
}

Now, the problem is with the ProcessEntity method. This is a generic method, that needs to retrieve the table of matching elements from the database according to the type or entity, so it looks like this:

public void ProcessEntity<T>(T entity)
{
  using( var repository = new DbRepository())
  {
    var set = repository.Set<T>();
    ...
  }
}

The problem is that the line var set = repository.Set<T>(); fails because T is ISomeInterface in this case, and not the actual type( A, B or C), so it gives an exception that is can't relate to the type given, which is understandable.

So my question is: How can i call ProcessEntity with the actual type of the object inside the list, and not the interfacetype that they implements.