I had this inspired idea of skill-trees into three Tiers: Root, Trunk, and a new 'Branch' extension.
Skill Tree
• Root (Tier 1 set - Class)
The Root is essentially the unlocking of class abilities that also helps distinguish newly-made cheating-hacker players in effort to remove them more quickly. It'd be a quick set of abilities to unlock where when completed you resume developing your individuality Trunk.
• Trunk (Tier 2 set - Role)
You'll have a clear route to progress through one of three or more Trunks. Each tree grows the same. The Trunk alters the Root abilities to support your decided role!
Using the example of the Infiltrator, ideally renamed Special Ops or something for this example, they'd tree into Infiltrate (melee), Reconnaissance (sniping) or Sabotage (bombs).
• Branch (Tier 3 set - Outfit)
The Branch extends the a Trunk's abilities to other classes within the Outfit somehow. This is outfit specialization.
The effect will help players decide who they're best parted with though this Branch should not segregate classes! Outfit 'Branch' specialization should benefit all members, all classes and all 'trunks' equally.