Shows a tree, with user-defined icons for some nodes. This tests listening for tree events. A separate alert is generated upon opening a folder that has contents; when opening a folder that has no contents; and closing a folder.
We also demonstrate changing the default value of 'allowShowPlusMinusSymbol' so that all folders initially have a plus/minus symbol. Then, upon opening an empty folder, we remove that icon.
Lastly, we demonstrate in the alert presented by tree events, use of the getHierarchy() method to obtain a full "path" for a tree node.