Like so many other species in Indiana, there is a native version and an alien version of Bittersweet. This is the alien version, Celastrus orbiculatus. The native version is called American Bittersweet (Celastrus scandens). In some parts of the U.S. the Oriental Bittersweet is an invasive problem. Around northeast Indiana, I’ve only seen it in a couple of places where it’s not really taking over at all. I’ve heard that it’s a real problem in the dunes area of northwest Indiana.
They look quite similar, but the leaves of the Oriental are more oval while American leaves are more pointy. The flower petals are different and the flower clusters of the Oriental emerge along the stem whereas they emerge from the end of the stems on the American.