I've finally been able to check material from the plant you photographed with material in the herbarium, and have just determined that it's Kunzea bracteolata, not K. ambigua as I first thought. One of its main characteristics is having head-like clusters of flowers at the end of branches. The flowers for Kunzea ambigua are crowded on leafy side branches or in the axils of upper leaves. Kunzea bracteolata is not native to the ACT, so remove any more that you may find.