An easy way to get this achievement, without playing through a character that dies before finishing three trees, is to create your own character on a new game with the Ruler Designer. To still be able to get achievements, points must be on or under 400 total spent. So as long as it is 400 or below, you can give yourself whatever traits/perks you want. This guide will be for unlocking the achievement through the Learning lifestyle.
For a safe location on the map, away from other rulers, I chose to create my ruler in Vestrland (western half of Iceland). I'd say it's the safest place on the map as it's so far away from anybody else and you only have to wipe out your eastern Icelandic neighbor to be at peace for probably the entirety of the game if you only stay on that island of Iceland.
Here's what I spent my points on:
Education: Mastermind Philosopher (+80)
Personality: Content (+20)
Other Traits: Genius (+240), Hideous (-30), Possessed (-20)
Skills: Lower any skill, other than Learning by -1 to get the max amount of points spent at 400.
I ended up getting the achievement by 909 AD at 60 years old. You can also go for reaching the highest devotion level for the (Saint) achievement as well as the one for creating a faith (It's not a Cult!), as Piety adds up quite a lot.
(Ended up getting 5769 Piety at 12.1 each month and the Saint achievement by 915 AD. Also don't forget to seek indulgences and go on pilgrimages if you're going for the other two achievements for more Piety!)