flutter_svg/example/assets/simple/nested_group.svg

<svg viewBox="0 0 120 120" 
  xmlns="http://www.w3.org/2000/svg">
  <g>
    <g fill="orange">
      <ellipse cx="60" cy="60" rx="50" ry="25" stroke="green" stroke-opacity=".3" />
    </g>
  </g>
</svg>