Hi! I’m new here and to bonsai. I picked up this new tree today and it came without identifying materials. So, I want to make sure I know what kind it is. Then, I’d also love any advice about how to care for this plant in Denver. Thank you for any help you can give!

Yes, as to Schefflera. Looks very much like mine. I have two bonsai schefflera as well as a houseplant and two that I have propagated. Beware they are prone to scales, even though mine are isolated, I noticed in the past few days scales have appeared. Bayer has a systemic fertilizer product that does get rid of them; that from my mentor Hal Sasaki.
Hope this helps.
It does look like that to. You will have to decide for yourself since you have the tree.
Perhaps a SCHEFFLERA We have some members who grow these. I don't have any my self.