string flysobigclass = "";
        string smallclass = ""; //小类
        TreeNodeCollection CheckedNodes = TreeView1.CheckedNodes;
        foreach (TreeNode t in CheckedNodes)
        {
            flysobigclass += t.Parent.Value + ",";
            smallclass += t.Value + ",";
        }
        string flysoStr = string.Empty;
        string[] flysoArrStr = flysobigclass.Split(',');
        if (flysoArrStr.Length > 0)
        {
            flysoStr = ",";
            for (int i = 0; i < flysoArrStr.Length; i++)
            {
                if (flysoStr.IndexOf("," + flysoArrStr[i] + ",") < 0)
                    flysoStr += flysoArrStr[i] + ",";
            }
            flysoStr = flysoStr.Substring(1, flysoStr.Length - 2);
        }
        string bigclass = flysoStr;//大类