This is a small code example I've done for Riff News
to demonstrate how to load data into a PHP-GTK GtkCTree from an external XML file:
http://www.riff.org/charger_un_gtkctree_depuis_xml_en_php-gtk
The (short) intro text is in french, but you can very well skip it to go directly to the code.
The example may also be useful in that the data being loaded into the tree represent the PHP-GTK 1 GTK class hierarchy (GDK not included).