I have this one level tree situation:
<select ng-model="tipost" 
        ng-options="tip.DESC group by tip.TIPIS for tip in tipall"><br>
</select>
where the json is: 
[
  {"ID":"1", "IDPARENT":"0", "TIPIS":"", "DESC":"GroupName1"},
  {"ID":"2", "IDPARENT":"1", "TIPIS":"GroupName1", "DESC":"CHILDNAME1"},
  {"ID":"3", "IDPARENT":"0", "TIPIS":"", "DESC":"GroupName2"}
]
the problem is that this creates the  optgroups with their children but repeats
the roots too:
- GroupName1
- GroupName2
[ GroupName1 ]
- CHILDNAME1
[ GroupName2 ]
i want to produce:
[ GroupName1 ]
- CHILDNAME1
[ GroupName2 ]