title: Treeview MVVM ObservableCollection Updates
body: <p>I have a treeview which binds to lots of nested ObservableCollections. Each level of the treeview shows an aggregated sum of all the hours in child items. For example:</p>
  
  <pre><code>Department 1, 10hrs
    ├ Team 10, 5hrs  
    │  ├ Mark, 3hrs
    │  └ Anthony, 2hrs   
    └ Team 11, 5hrs
       ├ Jason, 2hrs
       ├ Gary, 2hrs
       └ Hadley, 1hrs  
  Department 2, 4hrs   
    ├ Team 20, 3hrs  
    │  ├ Tabitha, 0.5hrs
    │  ├ Linsey, 0.5hrs
    │  └ Guy, 2hrs
    └ Team 11, 1hr
       └ "Hadley, 1hr"  
  </code></pre>
  
  <p>When I modify my <code>Individual.Hours</code> in my ViewModel class i want to update the <code>hours</code> 
  values in both my team and departments too. </p>
  
  <p>I'm already using <code>NotificationProperties</code> for all my <code>Hours</code> properties, and ObservableCollections for <code>Teams</code> in <code>Departments</code> and <code>Individuals</code> in <code>Teams</code>.</p>
  
  <p>Thanks,<br>
  Mark</p>