One thing you could consider is taking a path based approach to locating the tree node, like Main\Test Category B\B.1\T1 for example:

private TreeViewItem? FindItemByPath(TreeView treeView, string path)
{
    string[] nodes = path.Split(Path.DirectorySeparatorChar);
    ItemsControl currentLevel = treeView;
    foreach (string header in nodes)
    {
        bool found = false;
        foreach (var item in currentLevel.Items)
        {
            if (item is TreeViewItem treeViewItem && treeViewItem.Header.ToString() == header)
            {
                currentLevel = treeViewItem;
                found = true;
                break;
            }
        }
        if (!found)
        {
            return null;
        }
    }
    return currentLevel as TreeViewItem;
}

Regardless of how you find the item, what you then want to next is iterate up and expand all its parents.

private void SelectItem(TreeViewItem item)
{
    var parent = VisualTreeHelper.GetParent(item);
    while (parent is TreeViewItem parentItem)
    {
        parentItem.IsExpanded = true;
        parent = VisualTreeHelper.GetParent(parentItem);
    }
    item.IsSelected = true;
    item.BringIntoView();
}