Build JSON Hierarchy from Structured Data

After a troublesome fight i almost figured how to convert a flat json file to a Hierarchical one.

  list = [
    {
      id: 1,
      title: 'home',
      parent: null
    },
    {
      id: 2,
      title: 'about',
      parent: null
    },
    {
      id: 3,
      title: 'team',
      parent: 2
    },
    {
      id: 4,
      title: 'company',
      parent: 2
    }
  ]

  function treeify(list, idAttr, parentAttr, childrenAttr) {
      if (!idAttr) idAttr = 'id';
      if (!parentAttr) parentAttr = 'parent';
      if (!childrenAttr) childrenAttr = 'children';
      var treeList = [];
      var lookup = {};
      list.forEach(function(obj) {
          lookup[obj[idAttr]] = obj;
          obj[childrenAttr] = [];
      });
      list.forEach(function(obj) {
          if (obj[parentAttr] != null) {
              lookup[obj[parentAttr]][childrenAttr].push(obj);
          } else {
              treeList.push(obj);
          }
      });
      return treeList;
  };

  console.log(JSON.stringify(treeify(list)));