make std::ostream automatically ident when encountering special characters

I would like to have some facility which makes a std::ostream automatically ident on encountering special characters (or special objects). Let's assume that the special characters are < and >. In this case the following input test0<test1<test2> > should produce the following output:

test0<
    test1<
        test2
    >
>

How would one go to implement this?