angularjs expand & collapse issue

I am new in angularjs and currently i'm facing this issue.

Problem

when i clicked on any of the node, all the nodes will be expanded or collapsed. For example : (Before clicking on the node)

After clicking on the node

Code

 <div class="item">Data Visualization</div>
      <div class= "item">
           <i class="icon ion-arrow-right-b" ng-model="collapsed" ng-click="collapsed=!collapsed"><strong> &nbsp;AGV Mileage Vs Timestamp</strong></i>
           <div ng-show="collapsed.active">&nbsp;&nbsp; 

              <div id ="agvmileage">
                <div class = "horizon">
                    <canvas width="960" height="120">
                    <script src="/static/js/frontend/cubi-agv.js"></script>
                </div>
              </div>

           </div>
      </div>

      <div class= "item">
           <i class="icon ion-arrow-right-b" ng-model="collapsed" ng-click="collapsed=!collapsed"><strong> &nbsp;Board Temperature Vs Timestamp</strong></i>
           <div ng-show="collapsed">&nbsp;&nbsp; 

              <div id ="agvmileage">
                <div class = "horizon">
                    <canvas width="960" height="120">
                    <script src="/static/js/frontend/cubi-agv.js"></script>
                </div>
              </div>

           </div>
      </div>

      <div class= "item">
           <i class="icon ion-arrow-right-b" ng-model="collapsed" ng-click="collapsed=!collapsed"><strong> &nbsp;Laser Sensor Output Vs Timestamp</strong></i>
           <div ng-show="collapsed">&nbsp;&nbsp; 

              <div id ="agvmileage">
                <div class = "horizon">
                    <canvas width="960" height="120">
                    <script src="/static/js/frontend/cubi-agv.js"></script>
                </div>
              </div>

           </div>
      </div>

      <div class= "item">
           <i class="icon ion-arrow-right-b" ng-model="collapsed" ng-click="collapsed=!collapsed"><strong> &nbsp;Battery Current Vs Timestamp</strong></i>
           <div ng-show="collapsed">&nbsp;&nbsp; 

              <div id ="agvmileage">
                <div class = "horizon">
                    <canvas width="960" height="120">
                    <script src="/static/js/frontend/cubi-agv.js"></script>
                </div>
              </div>

           </div>
      </div>

And if possible, how can i declare the "data visualization" as parent node and others as child node.

Please enlighten me on this, thanks in advance.

via Kit