public void onModuleLoad() {
// Create a tree with a few items in it.
TreeItem root = new TreeItem("root");
root.addItem("item0");
// Add a CheckBox to the tree
TreeItem item = new TreeItem("foobarhogehoge"); // 長い文字列アイテム
item.addItem(new TreeItem("item11"));
item.addItem("item12");
item.addItem("item13");
item.addItem("item14");