Put Projects Into Folders?

As you can see in the sreenshot.

I have a Library with all Testimonial Interviews.
--- Then each event, is the interview with the specific client

But often times I with use parts of the interview to create Ads.  So I was hoping FCPX would let me put the Projects into folders.  Just to stay organized. And not have an ever scrolling list of Projects in that event.

As you can see from the highlighted selection in my screenshot, just one Ad, added 4 new projects.  I would Like to Put those in a new Folder titled "Ad 1"

Potentially Down the Line make another Folder titled "Ad 2"

Is this possible?  I know you can right click an event and select "add folder." but when I did that the folder wouldn't let me put any project inside of it...? 

A lot of users make an event just for holding all their projects. There is of course the Library Smart Collection for Projects.

Okay I can do that but that still doesn't solve my issue of having 4 very similar projects with slight edits.

Basically I want to put  a folder inside of a folder.  Or an event inside of an event.

What are those Folders meant to be used for (see screenshot)

Folders are you hold collections, keyword or smart collections. You could keyword the projects you want to group together or you could make a smart collection based on a name like Ad1.

how do I keyword a project?

Select the project in the event and press ⌘ K for the keyword editor.

Just adding Simon's terrific take on keywords and library organizations.

Tom Wolsky wrote:

Folders are you hold collections, keyword or smart collections. You could keyword the projects you want to group together or you could make a smart collection based on a name like Ad1.

What is a hold collection?

I failed to correct the mistyping. Folders are for holding collections

So I have opted to do the keyword, since it seemed the simplest for this situation (see screenshots).  But I still leaves me curious how I could use the actual folder feature? And why I would use it?  

If you could give me a step by step example that would be much appreciated

Add many keywords to clips in an event. In the browser there can now be a long, long list of keywords. Make folders and move groups on keywords into the folders so there are fewer, better organized groups of keywords in the event sidebar.

The lack of folders in the way Premiere uses them is really missed by many. Myself included. But the current solution to organize projects into smart collections. Set up criteria for your smart collection based on text including or excluding certain terms or phrases and then your projects will generally sort automatically. At the Event level you'll still see all the projects, but then as you step into individual smart collections it will only show those specific projects. For example, you can have a smart collection include all projects with "v1" in the name; then have a different smart collection with "v2" or "snapshot" or whatever.