First Tree

I would advise to ignore thinking about putting TP into the first tree, however, it will still be worth looking at to understand what is there. Better to know your class inside out, and if Slayer does ever get nerfed, or skills changed in that first tree. You will want to know the before and not just the after!
This is the defensive side, however doesn't offer enough defense to consider going for it.

Second Tree

The middle column, is offense. Mainly aimed towards dirks. But if you are swords don't panic!
The TP passive in this is nice, and also a nice stun, although it does hold you inplace. The reason I say it is aimed more towards dirks is because of the following.
TP passive Phase Blades which does offer equal P.Atk/M.Atk, so can go either way.
The TP Skill Envenom gives bonus damage based off your M.Atk, with swords this will be a very small bonus, however dirks it will be awesome!
The skill Twilight Strike offers a much larger bonus in damage towards M.Atk than P.Atk. If you use dirks you will hit far harder than those using swords. This skill here, is in my opinion the only reason to think about using dirks on a Slayer.

Third Tree

The 3rd and final column is also offensive.
You gain extra levels in your Assassin 'pewpew' Impact. This buff gives out so much damage, it is incredible!
Shadow Rush CD is reduced in the TP Passive, as well as getting to gain extra levels in the skill. This is extra helpful when you are in a party, although its bugged and you need to lay another skill before you attack or you will run back from where you came.
The TP skill Phantasm should only be taken if you are using swords. The bonus hits will be just as equal for both swords and dirks. However, dirks will get a bigger bonus from the Envenom skill in the middle tree. Swords offer more P.Atk and so technically will get more out of the additional hit.