Function flatten

src/cdk/tree/control/flat-tree-control.spec.ts:233–241

(nodes: TestData[], data: TestData[])

}

function flatten(nodes: TestData[], data: TestData[]) {
  for (let node of nodes) {
    data.push(node);

    if (node.children && node.children.length > 0) {
      flatten(node.children, data);
    }
  }
}