C# algorithm for generating hierarchy

C# algorithm for generating hierarchy

public static IEnumerable<Node<T>> Hierarchize<T, TKey, TOrderKey>(
    this IEnumerable<T> elements, 
    TKey topMostKey, 
    Func<T, TKey> keySelector, 
    Func<T, TKey> parentKeySelector, 
    Func<T, TOrderKey> orderingKeySelector)
    var families = elements.ToLookup(parentKeySelector);
    var childrenFetcher = default(Func<TKey, IEnumerable<Node<T>>>);
    childrenFetcher = parentId => families[parentId]
        .Select(x => new Node<T>(x, childrenFetcher(keySelector(x))));

    return childrenFetcher(topMostKey);

Utilizes this small node class:

public class Node<T>
    public T Value { get; private set; }
    public IList<Node<T>> Children { get; private set; }

    public Node(T value, IEnumerable<Node<T>> children)
        this.Value = value;
        this.Children = new List<Node<T>>(children);

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