Open a solution item in a new tab group in VSIX (visual studio extension)

[ghost]

I want to write an extension to open automatically the CSS file related to a LESS or SASS file in a new vertical tab group. It should create a new tab group if there is not any or use it if there is an existing tab group.

    void DoIt()
    {
        var dte2 = ((IServiceProvider)package).GetService(typeof(SDTE)) as EnvDTE80.DTE2;

        var currentActiveWindow = dte2.ActiveWindow;

        if (!IsItALessOrSassFile())
            return;

        var item = dte2.Solution.FindProjectItem(GetTheCssFileNameOfTheCurrentFile());
        item = item ?? throw new Exception();

        if (item.IsOpen)
            return;

        var window = item.Open();

        // I could not find any property or method to force the window to be opened in a new tab group.

        window.Activate();

        window.Document.ReadOnly = true;

        currentActiveWindow.Activate();            
    }

I mean the result should be somthing like this.