get tree width

const flattenChildren = (children) => children
  .reduce(
    (flattenedNextLevelChildren, child) => [...flattenedNextLevelChildren, ...child.children],
    []
  )

function getTreeWidth(tree) {
  let width = 1
  if (!tree.children.length) {
    return width
  }
  
  let flatChildrenList = tree.children
  
  while (true) {
    if (!flatChildrenList.length) {
      return width
    }
    width = width < flatChildrenList.length ? flatChildrenList.length : width
    flatChildrenList = flattenChildren(flatChildrenList)
  }
}

const width = getTreeWidth({
  value: 'root',
  children: [
    {
      value: '1_1',
      children: []
    },
    {
      value: '1_2',
      children: [
        {
          value: '1_2_1',
          children: []
        },
        {
          value: '1_2_2',
          children: [
            {
              value: '1_2_1',
              children: []
            },
            {
              value: '1_2_2',
              children: []
            },
            {
              value: '1_2_3',
              children: []
            },
          ]
        },
        {
          value: '1_2_3',
          children: [
            {
              value: '1_2_1',
              children: []
            },
            {
              value: '1_2_2',
              children: []
            },
            {
              value: '1_2_3',
              children: []
            },
            {
              value: '1_2_1',
              children: []
            },
            {
              value: '1_2_2',
              children: []
            },
            {
              value: '1_2_3',
              children: []
            },
          ]
        },
      ]
    }
  ]
})


console.log(width)