wpf + grouping listview

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WPF

ListView

grouping

Hello,
Below is the code currently i am using for grouping in listview. I am able to group records, but when user clicks on the button(AddNewCluster) to create new group with set of records i am unable to concatenate with the old records. The listview gets updated with the new group and records. But i need to show the user both the old and newly added group and records.

ListCollectionView collectionView; 
 
public Window1() 
{
InitializeComponent();
 
var clusters = new[] 
{
 
new Cluster { Name = "Front end" }, 
 
new Cluster { Name = "Middle end" }, 
 
new Cluster { Name = "Back end" }, 
};
collectionView =
new ListCollectionView(new[] 
{
 
new Server { Cluster = clusters[0], Name = "webshop1" }, 
 
new Server { Cluster = clusters[0], Name = "webshop2" }, 
 
new Server { Cluster = clusters[0], Name = "webshop3" }, 
 
new Server { Cluster = clusters[0], Name = "webshop4" }, 
 
new Server { Cluster = clusters[0], Name = "webshop5" }, 
 
new Server { Cluster = clusters[0], Name = "webshop6" }, 
 
new Server { Cluster = clusters[2], Name = "sql1" }, 
 
new Server { Cluster = clusters[2], Name = "sql2" }, 
});
 
var groupDescription = new PropertyGroupDescription("Cluster.Name"); 
 
// this foreach must at least add clusters that can't be  
 
// derived from items - i.e. groups with no items in them  
 
foreach (var cluster in clusters) 
groupDescription.GroupNames.Add(cluster.Name);
collectionView.GroupDescriptions.Add(groupDescription);
ServersList.ItemsSource = collectionView;
Clusters = groupDescription.GroupNames;
}
 
readonly ObservableCollection<object> Clusters; 
 
void AddNewCluster_Click(object sender, RoutedEventArgs e) 
{
Clusters.Add(NewClusterName.Text);
 
var clusters = new[] 
{
 
new Cluster { Name = NewClusterName.Text }, 
};
 
collectionView =
new ListCollectionView(new[] 
{
 
new Server { Name = "new server data" }, 
});
 
var groupDescription = new PropertyGroupDescription("Cluster.Name"); 
 
// this foreach must at least add clusters that can't be 
 
// derived from items - i.e. groups with no items in them 
 
foreach (var cluster in clusters) 
groupDescription.GroupNames.Add(cluster.Name);
collectionView.GroupDescriptions.Add(groupDescription);
ServersList.ItemsSource = collectionView;
}