I see you are using an article from our help that has not been properly updated through the years. We are very sorry for caused inconvenience and shall update the article to describe the best and most straightforward approach.
Meanwhile, I would like to suggest you use the BringPathIntoView feature of RadTreeView. You could find more info in the following article. The basic idea is to provide a full path from root to required item and RadTreeView will perform necessary expand and scroll operations in order to bring the item into view.
Additionally if you would like to select the item the best approach would be to use a binding to the IsSelected property as described in the following article.
Finally, I see you would like to use load on demand. This feature is targeting the scenario when user hits the expand arrow of particular item and the item currently does not have any children with concerns to performance. This will give the developer a chance to lazy load the required items and notify back the RadTreeView that items has been loaded.
In addition, when you would like to programmatically navigate to some item that has not yet been loaded you would have to load it manually. The load on demand will not take care to properly load required items. I.e. you would have to manually fill the required items' children collections. Then, after the data item has been loaded in the appropriate place (in RadTreeView items source) you could call the BringPathIntoView method and select the item programmatically (using the IsSelected binding to the view model).
Don't hesitate to contact us should you need more info on the topic.
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