godot-module-template/engine/editor/icons/Duplicate.svg

<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16"><path fill="#e0e0e0" d="m5 1v11h9v-6h-5v-5zm5 0v4h4zm-8 3v11h2 8v-2h-8v-9z"/></svg>