A major upgrade at Mosman High School has hit a milestone as the project team and school community celebrated the topping out of the new building.

With the upgrade starting to take its shape, the long-term tradition of a topping-out ceremony will involve a tree being lifted into place on the roof of the new construction.

As construction hits its highest point in the project, Member for North Shore Felicity Wilson joined all of those involved for the exciting ceremony for the community.

The upgrade is expected to be finished in 2023.