Syncing treeview diagram with another diagram

I want to create a treeview that is synced with my main diagram. The problem is, if I use the same model, the tree expander button defaults to using the linkDataArray to define what the parents and children are.

I could use a new TreeModel using the same data, I can define a “parent” property to use. However, my understanding is that the models will not be synced, and I still need to figure out how to use the existing “group” property I have in my nodeDataArray in place of the “parent” property.

Is there an easy way to define the property “group” as what to use? I’ve tried using nodeParentKeyProperty and setting that to “group” but the tree still tries to use linkDataArray to define the parents

Pretty rough example: http://codepen.io/anon/pen/GoyzJO
In this example, I would like Gamma Delta and Alpha to all be top level items, with Beta as a child of Alpha.

Thanks!

Like this sample? http://gojs.net/latest/samples/regroupingTreeView.html

Yup, just like that! Thank you!