It is the second breeding area, meaning you'll be able to breed dragons in the Breeding Mountain as well.
If you buy the Ultra Breeding Tree, it's good to have a Hatchery which has the upgrade 3 or 4.
Ultra Breeding Tree 2
On 14/5/2015, the Level-2 upgrade option for the Ultra Breeding Tree (and for the Breeding Mountain too) was released.
The upgrade will reduce the breeding time by 20%
For more info about breeding, please visit the Breeding page.