using System;

​

var instance = new Implementation();

var extInstance = new ExtImplementation();

​

instance.Foo();

extInstance.Foo();

​

((DocumentNode)extInstance).ExecuteTransaction();

Execute(instance);

Execute(extInstance);

​

void Execute(DocumentNode docNode) => docNode.ExecuteTransaction();

​

public interface ITransactions

{

    void ExecuteTransaction();

}

​

public class DocumentNode : ITransactions

{

    public void ExecuteTransaction() => Console.WriteLine("Base ExecuteTransaction");

    public ITransactions Transactions => (ITransactions) this;

}

​

public class ExtDocumentNode : DocumentNode, ITransactions

{

    public new void ExecuteTransaction() 

    {

        Console.Write("Overriden:");

        ((DocumentNode)this).Transactions.ExecuteTransaction();

    }

    public new ITransactions Transactions => (ITransactions) this;

}

​

public class Implementation : DocumentNode

{

    public void Foo() => this.Transactions.ExecuteTransaction();

}

​

public class ExtImplementation : ExtDocumentNode

{    

    public void Foo() => this.Transactions.ExecuteTransaction();

}