code for transforming data from multivariate format to the univariate format

data data;
infile 'c:\myfiles\testfile.dat';
input id y0 y1 y2 y3;
y=y0 trt=0; output;
y=y1 trt=1; output;
y=y2 trt=2; output;
drop y0-y2;
run;