You can find all about the Character Class Tree here
When you begin the game - you are entered into the Cave in Bootcamp - originally you were on the otherside of the map, until the Bane overrann the Control point, destroying practically everything, killing everyone they could. But still the AFS stayed, and chose the Cave with the hologram Eloh...
You start off at Level 1
and work up to Level 4
as a Recruit
Here you reach your first branch, do you choose the Soldier
path, or the Specialist
You stay as either class from Level 5
till Level 14
. If you chose the Soldier
Path, you'd then branch off to either a Commando
or a Ranger
. However if you chose the Specialist
path, you'd branch off to, Sapper
. From here you reach for final part of the tree, and one of the hardest for your main character...
You followed one of the branches and at Level 30
you can branch to either of the final part where you stay that class forever up to the max Level of 50
to a Grenadier
to a Sniper
to a Demolitionist
Remember once you reach each branch you can clone a character - so you can be a Solider and specialist at the same time!