how to put rectangle for labeled images?? which is labeled using CC = bwconncomp(BW)

i labeled an image using CC = bwconncomp(BW); and masking the label with maximum area using code

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

now i want to put thin rectangular box around that maximum area instead of masking it...how it can be done???