All skill perks spent in that tree are returned to your perk pool.
If you own The Elder Scrolls V: Skyrim Legendary Edition on Steam, the happens automatically. To force it: skyrim latest patch version 1.9.32.0.8 download
Whether you are a new player rediscovering the game or a veteran Dragonborn returning for another playthrough, ensuring that you are running version 1.9.32.0.8 is the first step toward the best possible experience. Keep your game updated through Steam, back up your saves, and consider adding the Unofficial Skyrim Legendary Edition Patch to catch what Bethesda missed. All skill perks spent in that tree are