If you are using milestones in your board and would like to visualize them in in your Gantt chart, Placker provides some options that will allow this type of customizing.
For example, if you click set layout, you can group the cards by milestone instead of the defaul mode, which is lists.
You can also click Filter & Settings and select Show milestones on top. This way, you will see the default layout of cards but with rows for milestones on top.
Another possibility is to select Show milestones markers, which will enable you to see a line on the column that refers to the date defined to that milestone.