Nobody followed that link? Watch the episode I linked in my first post. It's around the 18 minute mark. Geez, there's just no accounting for taste these days.
http://images1.wikia.nocookie.net/__cb20080807182643/castlevania/images/d/d9/Wakwaktree2.gifAs I said in my first post, the Wak Wak Tree in DoS has more in common with the Vampire Tree than the Islamic Wak-Wak Tree. That giant tree with weird heads from the Saturn SotN is closer to a Wak-Wak tree than the one in DoS.
@Inccubus: If I remember right (I forgot where the scene is in that episode, but I remember laughing at it), it says in kanji 吸血木 "blood-sucking tree". It was a play on 吸血鬼 (vampire). ... And a chupacabra is a 牛血鬼! (Not really, but it'd kinda fit.)
@Ratty: If it was indeed the Vampire Tree but just renamed the Wak Wak Tree, then what that means is Fleamen were originally a human sacrificed as fertilizer for the tree and as such the Fleamen are miniature versions of the sacrificed human.