I don't need the user workspaces in the navigation tree because it takes very long time to load the page.

I have tried the following but the user workspaces are stil shown in the explorer :

    <doctype name="Workspace" extends="Folder">
  <!-- for logo -->
  <schema name="file"/>
  <schema name="webcontainer"/>
  <schema name="publishing"/>
  <!-- the content of webcontainer -->
  <schema name="files" />
  <facet name="SuperSpace"/>
  <facet name="WebView"/>
  <facet name="HiddenInNavigation"/>
  <subtypes>
    <type>Workspace</type>
    <type>Folder</type>
    <type>File</type>
    <type>Note</type>
  </subtypes>
</doctype>