cosmosbulk.cs

 public async Task AddOrders(List<Order> orders, string customerId)
 {
  var ordersToInsert = new List<KeyValuePair<PartitionKey, Stream>>();
  foreach (var order in orders)
  {
    var stream = new MemoryStream();
    await JsonSerializer.SerializeAsync(stream, order);
    ordersToInsert.Add(new KeyValuePair<PartitionKey, Stream>(new PartitionKey(order.CustomerId), stream)); 
  }

  var parallelTasks = new List<Task>();

  foreach (var (key, value) in ordersToInsert)
  {
      parallelTasks.Add(this._cosmosDbContext.OrdersContainer.CreateItemStreamAsync(value, key)
      .ContinueWith(x =>
      {
        var response = x.Result;
        Console.WriteLine($"Bulk insert {response.ClientRequestId} has status {response.Status} with message {response}");
       }));
  }
  await Task.WhenAll(parallelTasks);
}