How about a Sunbonnet Sue on a tree swing. Just make the tree look like an oak. Or she could be raking up leaves that have fallen with lots of fall colors. Those are more applique ideas.
Here's some patterns from Quilter's Cache:
http://www.quilterscache.com/O/OakLeavesBlock.html
http://www.quilterscache.com/T/TreeE...tingBlock.html
http://www.quilterscache.com/T/Treeo...tionBlock.html
http://www.quilterscache.com/T/TreeofParadiseBlock.html
http://www.quilterscache.com/T/TreeofLifeBlock.html
http://www.quilterscache.com/T/TreesintheParkBlock.html
Or it can be whatever thinking of an oak tree reminds you of. I think of squirrels gathering the fallen acorns for winter. Or a summer picnic in the shade of a large oak tree at my Grandma's farm.
Good luck. I have the same problem with my guild challenge this year for a block on "freedom".