Ask Mr. Smarty Plants

 There are tree ferns that grow in New Zealand, Australia and some Polynesian islands, but none of the most common genera, Cyathea or Dicksonia, are shown by the USDA to occur in the wild in continental North America.  That doesn't mean that they don't occur in gardens, but the climate at the border of Tennessee and North Carolina is likely to be too cold for an escapee from a garden to survive.

Here are suggestions for native trees or shrubs that occur in the border area of Tennessee and North Carolina that could possibly be what you saw:

Rhus typhina (Staghorn sumac) has pinnately-compound leaves like a fern and there is even a cultivar called Cutleaf Staghorn sumac 'Laciniata' that makes it look even more fern-like.  Female plants are usually seen with clusters of red berries that form in the fall and persist through the winter.  Male plants, however, would not have berries.

Rhus glabra (Smooth sumac) also has pinnately-compound leaves and males would not show the red berries.  There is also a 'Laciniata' cultivar for this species, but they are females that would bear the red berries.  There is also a hybrid (Rhus x pulvinata) of R. glabra and R. typhina that has the cut leaves that look more fern-like.

Comptonia peregrina (Sweet fern) has fern-like leaves but it generally grows a low rounded bush with a maximum height of 4 feet. 

You can look through the native trees and shrubs that occur in the area by doing a COMBINATION SEARCH in our Native Plant Database and choosing North Carolina from the Select State or Province option and then 'Tree' or 'Shrub' under Habit (general appearance).   (I would pick North Carolina rather than Tennessee since you were traveling in the direction of North Carolina.)  Of course, you may have seen some non-native tree that I haven't thought of that wouldn't be in our Native Plant Database.