data = {{3, 2}, {6, 3}, {8, 10}, {9, 9},
   {3, 1}, {5, 2}, {6, 4}, {7, 8},
   {4, 1}, {7, 2}, {9, 0}, {10, 12}};

bc = BarChart[data, BarSpacing -> {0, 1}, PerformanceGoal -> "Speed",
   ChartStyle -> {LightOrange, LightGreen}, ImageSize -> 900, AspectRatio -> 0.4,
   ChartLabels -> {Flatten@ConstantArray[{"Mar", "Jun", "Sep", "Dec"}, 3], None},
   ImagePadding -> 8, PlotRangePadding -> {Automatic, {2, Automatic}}];

labels = MapThread[Inset[Style[#1, Bold, 16], {#2, -1.8}, {Center, Bottom}] &,
   {{"2015", "2016", "2017"}, {6.5, 18.5, 30.5}}];

selopts = {AspectRatio, Axes, AxesOrigin, ImageSize, PlotRangePadding};
opts0 = selopts /. bc[[2]];
opts = Thread[selopts -> opts0];
Graphics[bc[[1]], opts, Epilog -> Append[labels,
   Inset[SwatchLegend[{LightOrange, LightGreen}, Style[#, 12] & /@ {"Masha", "Bear"},
     LegendMarkerSize -> 20, LegendFunction -> (Framed[#, RoundingRadius -> 4,
         FrameStyle -> Gray] &)], {28, 10.5}]]]