updating xlswrite column for each iterartion

I'm trying to save .mat file data in xlswrite file. My first column have been updated. Now for second .mat file data should be in 2nd column of xls file. Below is my code

fid = fopen(fullfile(rt_data_dir, subname, [fname, '.mat']));

values = fread(fid);

xlswrite('FileName1.xlsx', values);

fclose(fid);