A question about Whirlwind

I know this is a very stupid question, but im really confusing about this skill, could anyone help me please?

1,My Assasin don't have any skill which named "Whirlwind", i even can unload a picture to proved it!

2,I searched over the internet as a result that i found, Assasin have no Whilrwind inside the skill tree.

3,Since there are no such skill "Whirlwind" for assasin, how can i build a WW Ghost Assassin?

I have no idea for this for this. My current version was 1.12a|||The "Chaos" Runeword (Fal Ohm Um) gives you +1 to WW.|||Thanks for the answer.|||I'm pretty sure Tienje mentions this in the ghost guide