Block to show sub-catagories from selected parent-catagorey.

As the title suggests, I am looking for a solution to show nested "sub-categories" from a selected "parent-category". Basically what the default "categories" block does but from a specific "parent-category". I'm using your plugin now and I think the logic is there, just needs a few tweaks.

I know Python quite well but I don't know PHP or javascript so I'm at a loss here. I'd be happy to help test it out in my site if that is of use.

Thank you!