Bias tape refers to a strip of fabric that is cut on the diagonal or bias of the cloth. It is used to finish the edges of garments or for decorative purposes. Full definition
This looks to me like it's probably done with strips of bias tape sewn together. (blog.colettehq.com)
I am using a baby blue with white polka dot cotton and have the same fabric in lime green that I'm planning to make bias tape from. (blog.colettehq.com)
Here's a tutorial you might like — there's actually a much faster (and easier) way to make bias tape. (blog.colettehq.com)