public virtual void createSkillTree(){
SkillTreeNode fb = addSkillTreeNode(typeof(FireballSkill), "Fireball", "Throw a fireball",
nodePositions[0], FireballModel.getImage());
SkillTreeNode ls = addSkillTreeNode(typeof(LightningStormSkill), "Lightning Storm", "...",
nodePositions[1], LightningModel.getImage());
SkillTreeNode cy = addSkillTreeNode(typeof(CycloneSkill), "Cyclone", "...",
nodePositions[2], HealModel.getImage());
// order: (parent, child)
fb.makeAvailable();
setSkillTreeNodeLinks(fb, ls);
setSkillTreeNodeLinks(fb, cy);
}