List Subfolders and files in treeview c#

private void ListDirectory(TreeView treeView, string path)
        {
            treeView.Nodes.Clear();
            var rootDirectoryInfo = new DirectoryInfo(path);
            treeView.Nodes.Add(CreateDirectoryNode(rootDirectoryInfo));
        }

        private static TreeNode CreateDirectoryNode(DirectoryInfo directoryInfo)
        {
            var directoryNode = new TreeNode(directoryInfo.Name);
            foreach (var directory in directoryInfo.GetDirectories())
                directoryNode.Nodes.Add(CreateDirectoryNode(directory));
            foreach (var file in directoryInfo.GetFiles())
                directoryNode.Nodes.Add(new TreeNode(file.Name));
            return directoryNode;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            foreach (var obj in opt.checkedListBox1.CheckedItems)
            {
                ListDirectory(treeView1, "E:\\mails\\" + obj);
               
                treeView1.ExpandAll();
            }

        }