A Redditor has gone ahead and constructed an image that maps out the complete Medical upgrade path. If you want to learn more about how leveling and character customization works in The Division, you can check out the piece we posted on that earlier.
The medical upgrade tree can give you multiple abilities, including the ability to carry more health packs, the ability to revive all allies in the area with a single drop ability, and the ability to cast a general healing wave that washes over all allied players in your general vicinity. Honestly, the Medical Wing upgrade path almost sounds like the most useful upgrade path in the game yet. You can check out the full upgrade tree below for yourself.