If you think Santiago Calatrava’s transportation hub and shopping mall looks like a bird (or a stegosaurus), you might find 3 World Trade Center next door reminding you of an upside-down Popsicle, with the stick at the top.

Its surprising profile — which is only temporary — results from a construction technique rarely used in New York office towers. The concrete core of the 69-story skyscraper is rising ahead of the steel columns and beams around its perimeter, sometimes 20 or more floors ahead.

On most office towers, structural completion is marked by a “topping out” in which the uppermost beam, signed by the workers, is raised to the building’s pinnacle. Things will be different in June at 3 World Trade Center.

“There will be a ceremony with workers signing the concrete bucket that will be hoisted to the top of the tower,” said Dara McQuillan, the chief marketing officer of Silverstein Properties, which is developing the building.