You need to find five treasure maps in Red Dead Redemption Undead Nightmare to level up as Treasure Hunter.
Before you go in search of these treasures across the plague land, you will need to find a map with locations of these treasures inside a camp with a box (You can find this map inside a chest at wilderness camp) When you have found the campsite and a map for these treasures, you can refer to this guide for the locations of all five treasures to level up as Undead Treasure Hunter.
Red Dead Redemption Undead Treasure Hunter Rank Video Guide- Treasure Maps Location Guide
Thanks. Typical Gamer