If you already a have structure created in the explore or finder for the folder, then you can simply import the parent folders in Lightroom and all the sub folders item will be imported as well with the same structure.
Also, please refer the link for more info: How to transfer photos from a hard drive folder to Photoshop Lightroom
You choose ADD (as opposed to Copy or Move) in the top menu of the Import window.
That leaves files in place on your Disk.
Thanks Geoff - perfect and simple.