Treeview expand only next sub level

I am using GoJs tree view. All the nodes in my tree view are expanded by default. My requirement is when i first load the tree view it should expand only to the first level. When i click expand icon against node then only one next level should be expanded.
Can you please modify treeview html file and send me?

I think you want to call Node | GoJS API. Something like:

    var root = myDiagram.findNodeForKey(...);
    myDiagram.nodes.each(function(n) { n.wasTreeExpanded = false; });