code: private void computeSiteSelector(HttpServletRequest request) {
  
          boolean selectorForType = TYPE_SIBLING.equals(getTreeType())
              || TYPE_COPY.equals(getTreeType())
              || TYPE_PAGELINK.equals(getTreeType())
              || TYPE_PREFERENCES.equals(getTreeType());
          boolean showFromRequest = Boolean.valueOf(request.getParameter(PARAM_SHOWSITESELECTOR)).booleanValue();
          if (selectorForType || showFromRequest) {
              // get all available sites
              int siteCount = OpenCms.getSiteManager().getAvailableSites(getCms(), true).size();
              setShowSiteSelector(siteCount > 1);
              return;
          }
          setShowSiteSelector(false);
      }
docs: Determines if the site selector frame should be shown depending on the tree type or the value of a request parameter.<p>
  
  If only one site is available, the site selector is not displayed.<p>
  
  @param request the HttpServletRequest to check