Sims 4 houses have multiple files and different file types - however they all go in the same folder:
This folder is for Lots and Sims
You can't make subfolders within the Tray folder and you should not rename any of the files you put there.
There are a few steps to do before you will see custom lots in your game gallery:
If you have not previously done so, open the Advanced option and check the box labeled 'Include Custom Content'