Photos Library

OS X EL Capitan Version10.11.2 MacBook Air

I want to make sure that I have all of my photos in one location. It looks as if I have 2 libraries in Finder and when I open PHOTO with the option key.

(1) Photos Library.photoslibrary 255.65GB

and

(2) Tree stand.photoslibrary 94.78GB .

Are the 2 libraries separate or do they contain the same pictures?

If they are separate; how can I merge them to one file?