Topsoil and sod

[mpatch]

Note that if roots are more than 6" deep in a lot of tree species they can suffocate. Many people lose their trees after adding a lot of soil cover. And they don't breathe through the bigger exposes roots. Just a FYI if you weren't aware, but for all I know your project already factors that.

That is very true. You can kill a perfectly healthy tree in short order by messing around with the grade around it.
OP post a picture of the tree and roots. There are a couple of options but burying the exposed roots is more than likely not one of them.

ETA 6 yds is a pretty goodly amount of dirt