Yes, there is another way.
In Safari, Go to Bookmarks/Show all bookmarks.
Now put all your bookmarks into a Folder (name it anything you want, it's only for this exercise).
Then left click-and-drag the folder onto the Desktop (it will copy it).
Open Folder on your Desktop and view it in List View. This automatically puts your Folder's contents in alphabetical order (in your case your bookmarks).
Now drag the Folder back into bookmarks. Open and check that all is well, then toss out the previous folder and delete same from Desktop.
For those who have already arranged their bookmarks into Folders, you can repeat this process with each one and end up with each Folder's bookmarks in alphabetical order.
Ian