It is beautiful.
Could it be two different color bouganvillas planted together? Bouganvillas have a vineing habit and can be trained to support themselves in a tree form.

Thank you. It is two bouganvillas. They were planted together, and now have cross bred if that's possible! Some of the flowers actually have both pink and white petals. We have a lot of people who stop by and take their picture under this tree!

Of course, bougainvilleas. I see that multi-colour isn't unusual:- (from Wikipedia)
"The actual flower of the plant is small and generally white, but each cluster of three flowers is surrounded by three or six bracts with the bright colors associated with the plant, including pink, magenta, purple, red, orange, white, or yellow".

Originated in Brazil but now found the world over. They were particularly common in the Cape (South Africa) when I lived there, and I've seen some lovely specimens on the Florida Keys.

Anyone know the best way to source/plant/propagate them? I think a couple would look good at my house.

A lovely cross popular in Hawaii is hot pink and orange..."sweet and sour"...beautiful!!!

You could cut a woody branch and stick it in garden soil, they don't really mind half sand. It would be much faster to buy largish established bound or potted plants. They need to be watered in the dry season but bloom best when it's hot and dry.
Like a poinsettia, the flower is just a tiny yellow center and the colorful "flower" are bracts.