cascading selects in angular

gistfile1.html

<div ng-controller="TeacherReportsController">
  <select ng-options="element.label for element in model" ng-model="firstOption"></select>
  <select ng-options="child.label for child in firstOption.children" ng-model="secondOption"></select>
  <select ng-options="child.label for child in secondOption.children" ng-model="thirdOption"></select>
  {{thirdOption.data}}
</div>