On Windows 10, the October 2018 Update (version 1809) installation process makes a copy of the current setup in the event that your device needs to undo the changes as a result of problems during the upgrade.
from https://www.windowscentral.com/how-reclaim-hard-drive-space-after-upgrading-windows-10-october-2018-update
https://www.windowscentral.com/sites/wpcentral.com/files/styles/large/public/field/image/2018/09/storage-settings-change-how-freeup-space-link.jpg?itok=4r_Ynbzh