Merging multiple GridFSDownloadStream into one

Question

How can I merge multiple GridFSDownloadStream so for example, I can send 10 images in one stream?

        var client = new MongoClient(configuration.GetConnectionString("MongoConnection"));
        var database = client.GetDatabase(configuration.GetConnectionString("MongoDatabase"));

        _bucket = new GridFSBucket(database, new GridFSBucketOptions
        {
            BucketName = "frames",
            ChunkSizeBytes = 1048576, // 1MB
            WriteConcern = WriteConcern.Unacknowledged,
            ReadPreference = ReadPreference.Primary
        });

        var ids = new List<string> { "1", "2", "3", "4", "5" };
        var streams = ids.Select(id => _bucket.OpenDownloadStreamAsync(new ObjectId(id)))
            .ToList();
        // how could I merge these streams here