Show the contents of Google Docs in tree format

The following code demonstrate use of Google Apps Script UI Services and DocList Services to display contents of a Google Docs Collection in Tree format.

 function doGet(e){    
  var app = UiApp.createApplication();  
  var scrollPanel = app.createScrollPanel(); // Scroll Panel is a Google Web Toolkit Widget  
  tree = app.createTree(); // Tree is a Google Web Toolkit Widget  
  tree.addItem(buildTree(app, "")); // <== you can put a filter or a specific directory  
  scrollPanel.add(tree);   
  scrollPanel.setHeight("500");  
  app.add(scrollPanel);  
  return app;  
 }  
 function buildTree(a, searchTerm){  
  var tree = a.createTreeItem(); // TreeItem is Google Web Toolkit Widget  
  tree.setText(searchTerm);  
  // Use of the Google Apps Script DocList Service to retrieve the collections.  
  var folders = DocsList.getFolder(searchTerm).getFolders();   
  for (var i = 0; i < folders.length; i++)  
    tree.addItem(buildTree(a, folders[i].getName())).setState(true, true);  
  var files = DocsList.getFolder(searchTerm).getFiles();  
  for (var i = 0; i < files.length; i++) {    
   if (files[i].getType() == "document") {  
    urlBase = "https://docs.google.com/document/edit?id=";  
    iconHTML = "https://docs.google.com/images/doclist/icon_7_document_list.png";  
   }   
   else if (files[i].getType() == "spreadsheet") {     
    urlBase = "https://spreadsheets.google.com/ccc?key=";  
    iconHTML = "https://docs.google.com/images/doclist/icon_7_spreadsheet_list.png";  
   }  
   else if (files[i].getType() == "presentation") {      
    urlBase = "https://docs.google.com/present/edit?id=";  
    iconHTML = "https://docs.google.com/images/doclist/icon_7_presentation_list.png";  
   }  
   else if (files[i].getType() == "drawing") {      
    urlBase = "https://docs.google.com/drawings/edit?id=";  
    iconHTML = "https://docs.google.com/images/doclist/icon_7_drawing_list.png";      
   }  
   else {  
    urlBase = "https://docs.google.com/fileview?id=";  
    iconHTML = "https://docs.google.com/images/doclist/icon_7_generic_list.png";    
   }    
   var image = a.createImage(iconHTML);  
   var fileLabel = a.createAnchor(files[i].getName(), urlBase+ files[i].getId());     
   var fileLabelPanel = a.createHorizontalPanel();  
   fileLabelPanel.add(image);  
   fileLabelPanel.add(fileLabel);     
   tree.addItem(fileLabelPanel).setState(true, true);  
  }    
  return tree;    
 }  

The ouput will be the following: