You can use ExpandAllHierarchyItems()/CollapseAllHierarchyItems() methods of RadGridView for hierarchy. Once you may get access to the GridViewToggleButton in you need to subscribe to the Checkec/UnChecked events of GridViewToggleButton and apply the appropriate logic:
sender, Telerik.Windows.Controls.GridView.RowLoadedEventArgs e)
var row = e.Row
var toggleButton = row.ChildrenOfType<GridViewToggleButton>().FirstOrDefault();
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