This achievement can be won by adding skill points to the same branch/section of your characters class tree until you unlock the ability that is furthest to the right on your screen.
In my case, my character is the pyromancer and I added skills in the firestorm skill tree taking the fastest path from left to right until I unlocked the Magma Elemental perk. I was able to unlock the achievement at level 21 (13 class points) which took about 19 hours for me. Time to complete will vary depending on how you play but that is a rough idea.
If you prefer to build your character to match your play style, you can build however you want and then use the Y button on the class tree to reset the class points when you are ready to get the achievement and allocate all of the points in the same section to get your achievement.