data={{{1.1,2.2}},
{{6.1,7.2},{7.2,8.3}},
{{4,3},{2,1}},
{{4,3},{2,1},{-1,-2},{3.9,10}},
{{1,3},{-6,-1},{-4,-5},{8,2},{-6,-6}}};
Column[IntervalUnion@@@Map[Interval,data,{2}]]