What treasure does Bilbo take from the dragon and why?

Because the dragon had taken the treasure from the dwarfs, so they wanted to reclaim as much of it as they could.

Answer:

Tolkien's dwarves are patterned after the Germanic and Norse dwarves. It is the nature of such dwarves to want as much treasure as they can get and keep it, this is much the same as the nature of dragons. Unlike dragons who saw the possession of gold as a good thing in itself and mostly sat and slept on their huge hoard, dwarves were skilled metal workers and viewed the treasure they hoarded as valuable for both its intrinsic value and its role as a raw material for their metal working. The magic of gold and jewels were essential for the amulets and weapons they produced.