text: vm.options = {
      childrenProperty: "nodes",
      expander: {
          type: "class",
          contracted: "hpe-add",
          expanded: "hpe-subtract"
      },
      icons: {
          type: "class",
          get: function (item, expanded) {
              // Use the childrenProperty to determine if it's a folder
              if (item.hasOwnProperty("nodes")) {
                  return expanded ? "hpe-folder-open" : "hpe-folder";
              }
              // Use file extension to select icon
              if (item.name.toLowerCase().endsWidth(".pdf")) {
                  return "hpe-document-pdf";
              }
              if (item.name.toLowerCase().endsWidth(".msg")) {
                  return "hpe-mail";
              }
              // ...
              return "hpe-document";
          }
      }
  };