fu-travis.js

const inArr = [
  { order: 0.1, depth: 1 },
  { order: 0.2, depth: 1 },
  { order: 0.3, depth: 2 },
  { order: 0.4, depth: 2 },
  { order: 0.5, depth: 1 },
  { order: 0.6, depth: 2 },
  { order: 0.7, depth: 3 },
  { order: 0.8, depth: 1 },
];

const treeIt = (arr, rootDepth = 1) => {
  return arr.reduceRight((acc, val) => {
    if (val.depth === rootDepth) {
      val.children = treeIt(acc.children, rootDepth + 1);
      acc.result.unshift(val);
      acc.children = [];
    } else {
      acc.children.unshift(val);
    }
    return acc;
  }, {
    result : [],
    children: []
  }).result;
};

console.log("result", treeIt(inArr));