Display list of posts in sidebar (organized by sub-category)

I need to display a specific category in my sidebar, beneath that, I want to show all its sub-categories and then all posts in each category. I also need to exclude posts in another category that may appear.

For example:

Parent Category
– Sub Category 1
— Post 1
— Post 2
-Sub Category 2
— Post 1
— Post 2

Here’s my code so far that works well, except I also want to exclude a certain category that might also appear in this list (either by name or ID):

[Code moderated as per the Forum Rules. Please use the pastebin]