A sunburst diagram displays a hierarchical structure. The origin of the organization is represented by the center of the circle, and each level of the organization by an aditional ring. The last level (leaves) are located at the extreme outer part of the circle. It is possible to map a numeric value to each leaf of the graphic, in this case their size will be proportional to this value. Sunburst diagrams suffer the same issue than pie or doughnut plot: it is really hard to compare the size of different slices and thus conveys poorly the information. You should probably consider treemap, circular packing or dendrogram.