Here is how the xml file bound to XmlDropDownList looks like:
<?xml version="1.0" encoding="utf-8"?>
<categories>
  <category name="Windows" id="5e9d7ec0-d395-11dc-95ff-0800200c9a66">
    <category name="Windows XP" id="40d2bab8-7c78-4e5b-adf5-3d9a76e38aec">
      <category name="Architecture" id="ab7aac45-8ceb-4400-9f62-40b69eab7514">
        <category name="x86-32" id="fe7a1a34-5f2b-45dd-8e23-c6a75717d216">
          <category name="Home Edition" id="7fcbdd73-a7dd-458e-9d1e-62f501bc5a7b"></category>
          <category name="Professional" id="1f5ae114-45bc-4b0b-b7f1-a15f451f9e65"></category>
          <category name="Tablet PC" id="3dfe28e2-5580-4be6-9d9d-d67cf3745f49"></category>
          <category name="Media Center" id="66c5c8f3-5b9c-4998-b8ff-7a1933243763">
            <category name="Media Center 2002" id="f71822b0-7c1a-4970-8a77-bc20b914ef9a"></category>
            <category name="Media Center 2003" id="b9fd8dea-05cd-4002-aad5-577396361e0a"></category>
            <category name="Media Center 2004" id="bb65f1d6-8c76-4d25-b84b-d5a28959e04c"></category>
            <category name="Media Center 2005" id="218ae289-84f0-4be8-9da9-bc95d8d0c853"></category>
          </category>
        </category>
        <category name="x86-64" id="aa555241-701b-4503-b541-58b5bc295775">
          <category name="Professional" id="05627a3d-43be-46aa-973f-200008609f4a"></category>
        </category>
      </category>
    </category>
    <category name="Windows Server 2003" id="5db9034a-7350-4bd1-84e4-f343e103de45">
      <category name="Architecture" id="a3c23252-ab83-4042-bf56-9069983b353b">
        <category name="x86-32" id="7a4a2d91-61a5-4815-8858-1f2ffb28c312"></category>
        <category name="x86-64" id="d0cb1584-eee5-4b63-a171-a28148bdcbe0"></category>
      </category>
      <category name="Platform" id="91c2bd8e-eb78-4053-9e1a-a9e52173b47b">
        <category name=".NET" id="f13f8485-cbc1-49d0-9edf-9e9d7b5402a9"></category>
        <category name="Java" id="3dfb1f29-f3c8-4687-82cd-7e883d7d99f1"></category>
        <category name="Native" id="3a0350e9-2ce9-45ff-83a3-e79db798e16a"></category>
      </category>
    </category>
    <category name="Windows Vista" id="78d31cde-c4e0-42e5-b2dd-b784f05fb115">
      <category name="Architecture" id="25364f6e-149c-41ee-b4f5-af97c5ed072d">
        <category name="x86-32" id="3ed6926c-6224-42d0-900e-e5cf17faf0ad"></category>
        <category name="x86-64" id="350729e7-604c-4b45-ac25-dc0e6e3532d7"></category>
      </category>
    </category>
  </category>
  <category name="Linux" id="8dcd8cde-fe24-4578-9c40-c21dd1d33d65">
    <category name="Distributions" id="66de1b1a-6e9a-4d19-9ebf-9e32f4d2982a">
      <category name="Debian" id="ed971204-36bf-49ad-a594-35cc2f0ff0ea">
        <category name="KDE" id="bd330495-e5cc-497a-85b9-484d43df16f9"></category>
        <category name="GNOME" id="0b9123a1-386a-4170-8003-d29be211a39f"></category>
      </category>
      <category name="Fedora" id="64dd5d7a-177c-4251-a8b4-26438f3b1f20"></category>
      <category name="KDE" id="0a42170a-ecde-4052-bc2d-c27f3556bcfd"></category>
      <category name="Knopixx" id="6c25bed6-2a9b-4ba1-be2a-a137089b0be1"></category>
      <category name="Mandriva" id="d867f8de-9a89-4daf-b783-fe22a23730d5"></category>
      <category name="RedHat" id="b08992af-b091-4b47-9b24-d809933d725a"></category>
      <category name="SuSE" id="d3f69a03-1d8f-43d6-9296-8e9805d43fab"></category>
      <category name="Ubuntu" id="f3953520-e5ea-4279-9c9b-6afa9ca70568"></category>
    </category>
    <category name="Platforms" id="0a8428b9-9333-49a5-8384-fab2d00466fb">
      <category name="Alpha" id="3a6343b2-1016-4685-8979-8227f4acaf3b"></category>
      <category name="ARM" id="b129a1bc-24e2-4065-9b1a-f47ff017a167"></category>
      <category name="Emdedded" id="6bb860e9-5e57-4fc7-b9db-250ba12bec6b"></category>
      <category name="PowerPC" id="e6024cf2-b195-40e8-abed-43b469c6e6b3"></category>
    </category>
  </category>
  <category name="Unix" id="d1ff66f6-e7eb-4023-bfeb-6830968e1b2d"/>
  <category name="Mac OS" id="2708f710-7564-4aeb-af34-b967c5c66973"/>
</categories>