You can use ItemsControl
(msdn) and specify ItemTemplate
:
<ItemsControl ItemsSource="{Binding}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Expander Header="{Binding Key}">
<ListBox ItemsSource="{Binding Value}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding ID}" />
<TextBlock Text="{Binding Name}" />
<TextBlock Text="{Binding Age}" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Expander>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>