Hierarchy: Heavy Metal

First let's find out what styles there are in Heavy Metal music. Here is some sources:
http://www.lastfm.de/out?url=http%3A%2F%2Fheavymetal.about.com%2F
Avant Garde Metal*
Black Metal*
Celtic Metal
Death Metal*
Doom Metal*
Gothic Metal*
Grindcore
Hair Metal
Metalcore
Nu-Metal
Power Metal*
Progressive Metal*
Thrash Metal*

http://en.wikipedia.org/
Avant-garde metal*
black metal*
death metal*
doom metal*
glam metal
gothic metal*
groove metal
power metal*
progressive metal*
speed metal
Stoner rock
symphonic metal
thrash metal*
viking metal

http://www.metal-archives.com/
Black*
Death*
Doom*
Electronic
Folk/Viking
Gothic*
Heavy/Traditional
Orchestral/Symphonic
Power*
Progressive*
Speed/Thrash*