The easiest way to achieve this is:
Right click the User Collection and choose New Folder.
In the Dropbox enter desired internal name and enter the same name in the text where it says Name of the new category.
Click OK.
Your new folder will appear under User Collection..
Right click your new folder and click edit folder, in the Dropbox your new folder path will be displayed in the Internal name box..
All you have to do is navigate to the folder and place your custom symbols there.
Refresh user collection by Right click user collection and select: Reload collections..and voila all your custom symbols will be available.