Treeview if node checked then

I am having difficulty with treeview and check boxes. I am attempting to have the root (parent) node checked if three or more child nodes are checked. I cannot seem to get the following code to work. I have tried many other variations but treeview does not seem to follow the other basic features such as checkbox fields. I can do this if i create a list of checkboxes on my own but not with a treeview. Thanks for all of your help!