I've always thought this was a dogwood tree -- but every time I use an online tree/shrub identification tool I come up empty handed.

This tree grows a huge amount of bluish like berries every few years, and the birds go crazy for them. It also grows pale-looking yellow flowers all summer and makes a huge mess.

(we built a treehouse around it)

Any clues?

Can you tell us where this tree is located?

Sacramento ... I think I've identified this as a Glossy Privet ... not easy to find.

That is certainly a big old Privet. Would be an invasive pest plant in eastern North America.