Inserts a new row before @sibling. If @sibling is %NULL, then the row will be appended to @parent 's children. If @parent and @sibling are %NULL, then the row will be appended to the toplevel. If both @sibling and @parent are set, then @parent must be the parent of @sibling. When @sibling is set, this function is called. To fill in values, you need to call gtk_tree_store_set() or gtk_tree_store_set_value().