C#

public interface IEdgeElement<N, E>
{
    int GetCost(TreeNode<N, E> ChildNode);
}


public interface INodeElement
{
}


public class Tree<N, E>
    where N : INodeElement
    where E : IEdgeElement<N, E>
{
    private List<EdgeConnector<N, E>> _EdgeList;

    public Tree()
    {
        _EdgeList = new List<EdgeConnector<N, E>>();
    }

    public int GetEdgeElementsCost()
    {
        int cost = 0;

        for (int i = 0; i < this._EdgeList.Count; i++)
        {
            cost = cost + this._EdgeList[i].Edge.Element.GetCost(this._EdgeList[i].ChildNode);
        }

        return cost;
    }
}


public class EdgeConnector<N, E>
    where N : INodeElement
    where E : IEdgeElement<N, E>
{
    private TreeEdge<N, E> _Edge = null;
    private TreeNode<N, E> _ChildNode = null;

    public TreeEdge<N, E> Edge
    {
        get
        {
            return _Edge;
        }
        set
        {
            _Edge = value;
        }
    }

    public TreeNode<N, E> ChildNode
    {
        get
        {
            return _ChildNode;
        }
        set
        {
            _ChildNode = value;
        }
    }

}


public class TreeEdge<N, E>
    where N : INodeElement
    where E : IEdgeElement<N, E>
{
    private E _Element;

    public TreeEdge(E Element)
    {
        this._Element = Element;
    }

    public E Element
    {
        get
        {
            return this._Element;
        }
    }
}


public class TreeNode<N, E>
    where N : INodeElement
    where E : IEdgeElement<N, E>
{
}