Showing icon of files (type of file) in tree view

I have used below code for structure of folders and files in server but I need icon of file (type of file) in tree view structure.

<pre>protected void Page_Load(object sender, EventArgs e)
    {
        if (Page.IsPostBack == false)
        {
            System.IO.DirectoryInfo RootDir = new System.IO.DirectoryInfo(Server.MapPath("~/Document/Detail Engineering/"));

            // output the directory into a node
            TreeNode RootNode = OutputDirectory(RootDir, null);

            // add the output to the tree
            TreeView1.Nodes.Add(RootNode);
            TreeView1.CollapseAll();
        }
    }

    TreeNode OutputDirectory(System.IO.DirectoryInfo directory, TreeNode parentNode)
    {
        // validate param
        if (directory == null) return null;

        // create a node for this directory
        TreeNode DirNode = new TreeNode(directory.Name);

        // get subdirectories of the current directory
        System.IO.DirectoryInfo[] SubDirectories = directory.GetDirectories();

        // output each subdirectory
        for (int DirectoryCount = 0; DirectoryCount < SubDirectories.Length; DirectoryCount++)
        {
            OutputDirectory(SubDirectories[DirectoryCount], DirNode);
        }

        // output the current directories files
        System.IO.FileInfo[] Files = directory.GetFiles();

      for (int FileCount = 0; FileCount < Files.Length; FileCount++)
       {
           string sFullname = directory.FullName;
           string sStr = sFullname + "\\" + Files[FileCount].Name;
           System.IO.FileInfo file = new System.IO.FileInfo(sStr);
           DirNode.ChildNodes.Add(new TreeNode(Files[FileCount].Name, Files[FileCount].Name));
          
           TreeNode subnode = new TreeNode(Files[FileCount].Name);
           string test = subnode.ValuePath;
          subnode.NavigateUrl = sStr;
          subnode.SelectAction = TreeNodeSelectAction.Select;

           


        }

        // if the parent node is null, return this node
        // otherwise add this node to the parent and return the parent
        if (parentNode == null)
        {
            return DirNode;
        }
        else
        {
            parentNode.ChildNodes.Add(DirNode);
            return parentNode;
        }
    }