Misleading documentation around multiple select; feature request for multi select

Thanks for your great module.

The documentation suggests support for multiple select, but this is not really so in that the multiple select does not behave the way a normal drupal multiple-select works. This wasted a bit of time as I tried to chase down what I was missing. This was exacerbated a little by comments in the code that mention 'multiple hierarchy vocabularies,' which after looking at the code I came to understand is not the same as multiple select hierarchy vocabularies.

A feature request:
A nice design would be to render a new select list when something is selected in the first select list, or render a "select more..." that would trigger a new dropdown. Seems like one could do this with a drupal form. I would like to code this but I don't think I have the time right now.