Adding a plot line (trend) to a group of bars

I have generated the following groups of bars in Matlab (v.2015b).

Now for each group of bars I want to plot a line, that represents some more information about each group. For example, a single group (D1 for example) must look like this:

Answer 1

[KSSV]

A = randn(1000,1);
h = hist(A) ;
bar(h)
hold on
plot(1:length(h),h,'r')

[Osh]

This works if I had a single bar group (or simply one single bar chart). How do I repeat this plot line for each of the groups (D1,D2,D3,D4..D6) in the above multi-group graph?

[KSSV]

Run it for each group...use hold on to plot.