filterTree.js

app.filter("filterTree", [
  "$filter", function($filter) {
    return function(tree) {
      var newTree = [];
      angular.forEach(tree, function(node, index) {
        var newNode;
        newNode = {
          id: node.id,
          sort_order: index,
          children: $filter('filterTree')(node.children)
        };
        newTree.push(newNode);
      });
      return newTree;
    };
  }
]);