var whereCondition = string.Format("NodeSKUID = {0}", skuid);
// Ignore linked nodes
whereCondition = SqlHelper.AddWhereCondition(whereCondition, "NodeLinkedNodeID is null");
var tree = new TreeProvider(MembershipContext.AuthenticatedUser);
var nodes = tree.SelectNodes(SiteContext.CurrentSiteName, string.Empty,LocalizationContext.PreferredCultureCode, false, null, whereCondition, orderBy, -1, true, 1);
That might help.