async function fetchRecursive(base_url, arr) {
  const result = [];
  const promises = [];

  if (Array.isArray(arr))
    for (const n of arr) {
      if (n.children) {
        let ch_arr;
        try {
          const data = {
            id: n.id,
            externalId: n.externalId,
            text: n.text,
            children: fetch(base_url + n.id).then((r) => {
              ch_arr = { ...r };
              return r.json();
            }),
            productCount: n.productCount,
          };

          data.children.then(children => data.children = children);
          promises.push(data.children);

          result.push(data);
        } catch (error) {
          result.push({ id: n.id, error });
        }
        result.push(...(await fetchRecursive(base_url, ch_arr)));
      } else {
        result.push(n);
      }
    }

  await Promise.all(promises);
  return result;
}