Script that uses EWS to create a top-level folder and then create sub-folders in the top-level folder?

Exchange 2010 SP2, Windows 2008 R2. I have been playing with EWS in hopes that I can meet the goals my client would like to achieve.  For newly created mailboxes, I need to create a root-level folder which contains several sub-folders. I have been able to script the creation of a SINGLE folder and I need assistance with the sub-folder creation. Here is the script I am using to create the parent folder and if you could please tell me what I need to add in order to create multiple sub-folders.

function CreateFolder($MailboxName)
{
    #Change the user to Impersonate
    $service.ImpersonatedUserId = new-object Microsoft.Exchange.WebServices.Data.ImpersonatedUserId([Microsoft.Exchange.WebServices.Data.ConnectingIdType]::SmtpAddress,$MailboxName);

    #Create the folder object

 $oFolder = new-object Microsoft.Exchange.WebServices.Data.Folder($service)
    $oFolder.DisplayName = $FolderName

    #Call Save to actually create the folder
    $oFolder.Save([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::msgfolderroot)

    $service.ImpersonatedUserId = $null
}

#Change the name of the folder
$FolderName = "My Custom Folders"
Import-Module -Name "C:\Program Files\Microsoft\Exchange\Web Services\1.2\Microsoft.Exchange.WebServices.dll"

$service = New-Object Microsoft.Exchange.WebServices.Data.ExchangeService([Microsoft.Exchange.WebServices.Data.ExchangeVersion]::Exchange2010_SP2)

# Set the Credentials
$service.Credentials = new-object Microsoft.Exchange.WebServices.Data.WebCredentials("username","password","domain")

# Use AutoDiscover
$UseAutoDiscover = $true
$a = get-mailbox "alias"

$a | foreach-object {
    $WindowsEmailAddress = $_.WindowsEmailAddress.ToString()

    CreateFolder($WindowsEmailAddress)
}