Sample Code

    t = DTree(unique=False)
    sql = f'SELECT id, name FROM country WHERE code2="CA" ORDER BY name;'
    if app.db.execute(sql):
        for country_row in app.db.fetchall():
            country_id, name = country_row
            country_node = Node(name=name.strip(), parent=t)

            sql = f'SELECT id, name FROM country_zone WHERE country_id=%s ORDER BY name;'
            if app.db.execute(sql, (country_id, )):
                for zone_row in app.db.fetchall():
                    zone_id, name = zone_row
                    zone_node = Node(name=name.strip(), parent=country_node)

                    sql = f'SELECT id, name FROM country_place WHERE zone_id=%s ORDER BY name;'
                    if app.db.execute(sql, (zone_id, )):
                        for place_row in app.db.fetchall():
                            place_id, name = place_row
                            Leaf(name=name.strip(), parent=zone_node)

        t.query('Canada/Ontario').show()