how to draw rectangle for biggest labeled area in an image??

i labeled an image using CC = bwconncomp(BW). and found the biggest area labeled using

numPixels = cellfun(@numel,CC.PixelIdxList);
[biggest,idx] = max(numPixels);
BW(CC.PixelIdxList{idx}) = 0;

now how can i put rectangle for biggest area??