I wanted to create some subdirectories inside my blob. But it is not working out well

Here is my code

protected void ButUpload_click(object sender, EventArgs e)
    {
        // store upladed file as a blob storage
        if (uplFileUpload.HasFile)
        {
            name = uplFileUpload.FileName;
            // get refernce to the cloud blob container
            CloudBlobContainer blobContainer = cloudBlobClient.GetContainerReference("documents");

            if (textbox.Text != "")
            {
                name = textbox.Text + "/" + name;
            }
            // set the name for the uploading files
            string UploadDocName = name;

            // get the blob reference and set the metadata properties
            CloudBlockBlob blob = blobContainer.GetBlockBlobReference(UploadDocName);
            blob.Metadata["FILETYPE"] = "text";
            blob.Properties.ContentType = uplFileUpload.PostedFile.ContentType;

            // upload the blob to the storage
            blob.UploadFromStream(uplFileUpload.FileContent);

        }
    }

What I did is that, If I have to create a sub directory, I will enter the name of the sub directory in the textbox.

for example, if I need to create a file named "test.txt" inside the sub directory "files" Then, my textbox.text = files and uplFileUpload.FileName = test.txt

Now I will concatenate them and upload to the blob.. But it is not working well.. I am getting just https://test.core.windows.net/documents/files/

I am not getting the entire thing I was expecting https://test.core.windows.net/documents/files/test.txt

What am I doing wrong... How to create sub directories inside the blob.