If you are willing to move up to Perl/Gtk2, it has a nice editable treeview.

#! /usr/bin/perl -w

use strict;
use Gtk2 '-init';
use Glib qw/TRUE FALSE/;

#standard window creation, placement, and signal connecting
my $window = Gtk2::Window->new('toplevel');
$window->signal_connect('delete_event' => sub { Gtk2->main_quit; });
$window->set_border_width(5);
$window->set_position('center_always');

#this vbox will geturn the bulk of the gui
my $vbox = &ret_vbox();

#add and show the vbox
$window->add($vbox);
$window->show();

#our main event-loop
Gtk2->main();
######################################################################
+##

sub ret_vbox {

my $vbox = Gtk2::VBox->new(FALSE,5);
$vbox->set_size_request (300, 300);

    #this is one of the provided base Gtk2::TreeModel classes.
    my $tree_store = Gtk2::TreeStore->new(qw/Glib::String/);

    #fill it with arbitry data
    foreach (1..3) {
    
        my $parent_nr = $_;
        
        my $iter = $tree_store->append(undef);
        $tree_store->set ($iter,0 => "Parent $parent_nr");
        
                 foreach (1..3){
            my $iter_child = $tree_store->append($iter);
            $tree_store->set ($iter_child,0 => "Child $_ of Parent $pa
+rent_nr");
        }
    }
    
    #this will create a treeview, specify $tree_store as its model
    my $tree_view = Gtk2::TreeView->new($tree_store);

        #create a Gtk2::TreeViewColumn to add to $tree_view
        my $tree_column = Gtk2::TreeViewColumn->new();
        $tree_column->set_title ("Click to sort");
        
            my $renderer = Gtk2::CellRendererText->new;
            
            $renderer->set_property('editable' => TRUE);
            
            $renderer->signal_connect (edited => \&cell_edited, $tree_
+store);
            
        $tree_column->pack_start ($renderer, FALSE);
        
        $tree_column->add_attribute($renderer, text => 0);
    
    #add $tree_column to the treeview
    $tree_view->append_column ($tree_column);
        
$vbox->pack_start($tree_view,TRUE,TRUE,0);
$vbox->show_all();
return $vbox;
}

sub cell_edited {
  my ($cell, $path_string, $new_text, $model) = @_;
  
  my $path = Gtk2::TreePath->new_from_string ($path_string);

      my $column = $cell->get_data ("column");
    my $iter = $model->get_iter ($path);
  
  $model->set_value ($iter, $column, $new_text); 
}
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