<?php
$menu = entity_create('menu', array('id' => 'a7', 'label' => 'a7'));
$menu->save();

$i = 0;

$m1 = entity_create('menu_link', array(
  'menu_name' => $menu->id(),
  'link_title' => 'hey' . $i++,
  'route_name' => 'node.view',
  'route_parameters' => array('node' => 1),
  ));
$m1->save();

$m2 = entity_create('menu_link', array(
  'menu_name' => $menu->id(),
  'link_title' => 'hey' . $i++,
  'plid' => $m1->id(),
  'route_name' => 'node.view',
  'route_parameters' => array('node' => 1),
  ));
$m2->save();

$m3 = entity_create('menu_link', array(
  'menu_name' => $menu->id(),
  'link_title' => 'hey' . $i++,
  'plid' => $m2->id(),
  'route_name' => 'node.view',
  'route_parameters' => array('node' => 1),
  ));
$m3->save();

$m4 = entity_create('menu_link', array(
  'menu_name' => $menu->id(),
  'link_title' => 'hey' . $i++,
  'plid' => $m3->id(),
  'route_name' => 'node.view',
  'route_parameters' => array('node' => 1),
  ));
$m4->save();