How to select multiple bubbles in quadrant chart?

Hi everyone,

I wanted to alter quadrant chart, so I will be able to select multiple bubbles. As I understood from selectionmanager tutorial in github, to be able for multiple selection, in selection should be added true.  This approach does work in my custom visual. However, in this particular visual, it does not work. What can be the issue? Also, is it possible to select multiple bubbles by selecting area on chart?