public TreeNodeProvider(string referenceId)
            : base(referenceId)
        {
            TestTreeNode._count = 0;

            _nodes = new Dictionary<string, TestTreeNode>();

            var knud = new TestTreeNode("Knud", _nodes);
            knud.Add(_nodes, "Louise", "Rikke", "Sofie", "Jeppe");
            var louise = knud.Children.First();
            louise.Add(_nodes, "Mathias", "Kasper", "Rasmus");
            var jeppe = knud.Children.Last();
            jeppe.Add(_nodes, "Villads", "Emma");
        }