I'm not quite sure what do you mean. However, you can add IsExpanded
property in your business class/ view model and bind it to the TreeViewItem via style. Then you can change it's status to IsExpanded when you need to. For your convenience I implement this approach in the attached project. Please take a look at it and let us know if this works for you. If not - please provide us more detailed information or modify the sent project to show us your scenario.
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