assertion `VALID_ITER (parent, tree_store)' failed?

[Micheal Smith <xulfer cheapbsd net>]

I'm trying to add something to a treeview based on a row reference.  
However when I try to do this I keep getting the error referenced within 
the subject.  Perhaps I'm doing something wrong, but I can't figure it 
out for the life of me.

Here is some test code I wrote up...

static void
populate_leftpane(GtkWidget *leftpane_treeview,
                  struct interface_data *intdata) {
    GtkTreeStore *treestore;
    GtkTreeIter toplevel, child;
    GtkTreeViewColumn *col;
    GtkTreePath *path;
    GtkTreeRowReference *ref;
    GtkCellRenderer *renderer;
    GtkTreeSelection *selection;

    col = gtk_tree_view_column_new();
    gtk_tree_view_append_column(GTK_TREE_VIEW(leftpane_treeview), col);
    renderer = gtk_cell_renderer_text_new();
    gtk_tree_view_column_pack_start(col, renderer, TRUE);
    gtk_tree_view_column_add_attribute(col, renderer, "text", 0);

    treestore = gtk_tree_store_new(1, G_TYPE_STRING);

    gtk_tree_store_append(treestore, &toplevel, NULL);
    gtk_tree_store_set(treestore, &toplevel, 0, "Test1", -1);

    gtk_tree_store_append(treestore, &toplevel, NULL);
    gtk_tree_store_set(treestore, &toplevel, 0, "Test2", -1);

    gtk_tree_store_append(treestore, &toplevel, NULL);
    gtk_tree_store_set(treestore, &toplevel, 0, "Test3", -1);
    path = gtk_tree_model_get_path(GTK_TREE_MODEL(treestore), &toplevel);
    ref = gtk_tree_row_reference_new(GTK_TREE_MODEL(treestore), path);
    gtk_tree_path_free(path);
    intdata->playlist_node_ref = ref;

    // I know this code isn't very useful, but I'm just attempting to 
use this
    // to test / describe my issue.
    path = gtk_tree_row_reference_get_path(ref);
    gtk_tree_model_get_iter(GTK_TREE_MODEL(treestore), &toplevel, path);

    // The following line is what triggers the failed assertion.
    gtk_tree_store_append(treestore, &toplevel, &child);
    gtk_tree_store_set(treestore, &toplevel, 0, "Testing", -1);

    gtk_tree_view_set_model(GTK_TREE_VIEW(leftpane_treeview),
                            GTK_TREE_MODEL(treestore));

    selection = 
gtk_tree_view_get_selection(GTK_TREE_VIEW(leftpane_treeview));
    gtk_tree_selection_set_mode(selection, GTK_SELECTION_BROWSE);
}

Any comments, or suggestions would be appreciated.