I have created a sample project based on the help article you are referencing. Could you please take a look at the attached project and check whether it is working for your case?
As far as I understand you would like to select and item in the TreeView using a binding to the SelectedItem property. If that is the case, I hope the sample will be of help to you. Otherwise, could you please modify the sample in order to introduce the issue you are facing or provide us a bit more info about your scenario?
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