This is what I have in the page load:

if (!IsPostBack)        {

        foreach (var nodeStructure in ListStructure)

                {

                    DataTreeNode nodo = new DataTreeNode();

                    nodo.Attributes.Add("Estructura", nodeStructure.Id.ToString());

                    nodo.Text = nodeStructure.Nombre;

                    LoadHierarchy(nodo, nodeStructure);

                    tree.Nodes.Add(nodo);
                }

var nodes = from DataTreeNode nodo in tree.AllNodes
                            where !string.IsNullOrEmpty(nodo.Key)
                            select nodo;

                int order = 1;
                foreach (DataTreeNode nodo in nodes)
                {
                    nodo.Attributes.Add("Order", order.ToString());
                    order++;
                }

}

And this is the recursive method:

private void LoadHierarchy(DataTreeNode nodoPadre, ModuloContenido contenidoPadre)
    {
        foreach (var nodoContenidoHijo in contenidoPadre.ColModuloContenidoHijos)
        {
            DataTreeNode nodoHijo = new DataTreeNode();
            nodoHijo.Attributes.Add("Estructura", nodoContenidoHijo.IdModuloContenido.ToString());
            nodoHijo.Text = nodoContenidoHijo.Nombre;
            ArmarJerarquia(nodoHijo, nodoContenidoHijo);
            nodoPadre.Nodes.Add(nodoHijo);
        }
    }

After a click in the node, the attributes are missing, but not all of them, the "Order" attribute still remains.

Thanks in advance for the help.