GtkCTree::node_set_pixtext

void node_set_pixtext( GtkCTreeNode node , int column, string text, int spacing, GdkPixmap pixmap , GdkBitmap mask );

Sets the pixmap and the corresponding text of a column of a row. The pixmap and mask parameters may not be NULL.

If you once expand/collapse the node, the icon is gone because the open/closed icons you set at the insert_node are used then. To prevent this, use the set_node_info function. The text stays visible.