WPF TreeView bound to ObservableCollection won't update when adding

WPF TreeView bound to ObservableCollection won't update when adding

Have browsed similar answers, but I just can't find the problem.
I'm using MvvmLight, and have bound a WPF TreeView to an
ObservableCollection in the ViewModel. The tree shows fine, but if I add
members to the ObservableCollection later on, the tree doesn't refresh.
Here's the code:
// the data type that represents a tree node
public class FurnitureTreeNode : GalaSoft.MvvmLight.ViewModelBase
{
public string Name { get; private set; }
public object Data { get; private set; }
public ObservableCollection<FurnitureTreeNode> ChildNodes { get; set;}
public Furniture(string Name, ObservableCollection<FurnitureTreeNode>
ChildNodes, object Data)
{
this.Name = Name;
this.ChildNodes = ChildNodes;
this.Data = Data;
}
}
public class FurnituresViewModel : GalaSoft.MvvmLight.ViewModelBase
{
public ObservableCollection<FurnitureTreeNode> TopFurnitureNodes {
get; set; }
public ObservableCollection<FurnitureTreeNode> ChairNodes { get; set; }
public FurnituresViewModel() : base("Furnitures")
{
// initialize the top level furnitures collection
TopFurnitureNodes = new ObservableCollection<FurnitureTreeNode>();
// add two children
TopFurnitureNodes.Add(new FurnitureTreeNode("Tables", null, null);
TopFurnitureNodes.Add(new FurnitureTreeNode("Chairs", null, null);
// add Beds only when they're ready
BedsManager.ImportsSatisfied += AddBedsNode;
}
The following runs fine, the collection is updated with the Beds node, but
it isn't reflected in the TreeView:
void AddBedsNode( object sender, EventArgs e )
{
Task.Run(() =>
{
TopFurnitureNodes.Add(new FurnitureTreeNode("Beds", null, null);
}
);
}
}
Here's the XAML:
<TreeView Name="FurnituresTreeView" ItemsSource="{Binding
TopFurnitureNodes}">
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Path=ChildNodes}"
DataType="x:Type FurnitureTreeNode">
<TextBlock Text="{Binding Path=Name}" />
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>
Thank you!