Hi @MarkTEvans,
I suggest you try using the "gear" button on the native Gantt View to toggle Milestone Diamonds and/or Milestone Lines on or off, which might meet your "roll up into a single line" requirement.
Alternatively, if you need more control (e.g. over the appearance, sorting, level of detail, colors, page size, etc.), I invite you to consider our Roadmap solution, which lets you tag existing Tasks with data driven bar colors, fonts, and icons to efficiently generate real time professional Roadmap reports at various levels of detail.
Regards,
Doug
TIP: if this solved your problem, I invite you to consider marking it as a Correct Answer to help others who might also find it of use