code: function (parentMenuTree) {
                  if (!parentMenuTree) {
                      return null;
                  }
                  return _.sortBy(
                      _.compact(
                          _.filter(_.values(parentMenuTree), function (elt) {
                              return _.isArray(elt);
                          }).concat(_.map(_.compact(parentMenuTree), 'route'))
                      ),
                      function (elt) {
                          if (_.isArray(elt)) {
                              return elt.categoryPosition || 0;
                          } else {
                              return 1000000 + elt.sortKey || 0;
                          }
                      });
              }
docs: @ngdoc function
  @name w20CoreUI.service:NavigationService#computeSubTree
  @methodOf w20CoreUI.service:NavigationService
  @param {Object} parentMenuTree The parent tree
  @returns {Object} The subtree of a parent tree
  
  @description
  
  Given a parent tree this function will compute the underlying subtree. This function is used to
  determine the deeper level of themes sidebar tree in a recursive way.