At least provide the code you are using now and some example data.
Also does your data always have exactly 2 bars in each "cluster"? If not then this may be a meaningless task. Depending on your data you may also appear to have "missing" bars if the value for the height is 0.
Example of "missing bar".
data example;
input xvar groupvar responsevar;
datalines;
1 1 3
1 2 4
2 1 6
2 2 0
2 3 2
;
run;
proc sgplot data=example;
vbar xvar/group=groupvar response= responsevar
groupdisplay=cluster
;
run;