The Christmas tree tradition of decorating an evergreen tree with ornaments and garland began in Germany in the 16th century.   I decided this year that I would make a garland from popcorn and cranberries to put around the tree.  Look at the pattern I used for stringing popcorn and cranberries and try to figure out what the next 6 items will be on the garland.
I am using P for popcorn and C for a cranberry.

            P-C-P-C-P-P-C-P-C-P-C-P-P-C-P-C-P-P-C-P-C-P-C-P-

Hint : Take a look at the keys on a piano keyboard.