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HTML 

              
                <!--
  Forked from:
  http://localhost:9090/vue-components/select#Example--Option-group
  To Do: Recursive expansion of nested children
  See https://codepen.io/mickey58/pen/yLJEJNG 
  
  New feauture added below:
    - Allow selection of first level (group), not only selection of a child
    - Done by @click="model = scope.opt.label"
   -  Problem: This does not work in combination with expand-icon-toggle 
      (which in  theory should allow selection of an item on first level from its   expansion)

  Note: With selection 'multiple', the simple "model = value" needs to be replaced
  by an array push operation
-->
<div id="q-app">
  <div class="q-pa-md" style="max-width: 300px">
      <div class="q-gutter-md">
        <q-badge color="secondary" multi-line>
          model: "{{ model }}"
        </q-badge>
  
        <q-select
          filled
          options-dense
          v-model="model"
          :options="options"
          label="Standard"
          color="teal"
          clearable
          options-selected-class="text-deep-orange"
          
        >
          <template v-slot:option="scope">
            <q-expansion-item
              dense
              expand-separator
              group="somegroup"
              :default-opened="hasChild(scope)"
               header-class="text-weight-bold"
              :label="scope.opt.label"
              @click="model = scope.opt.label"
            >
              <template v-for="child in scope.opt.children">
                <q-item
                  dense
                  :key="child.label"
                  clickable
                  v-ripple
                  v-close-popup
                  @click="model = child.label"
                  :class="{ 'bg-light-blue-1': model === child.label }"
                >
                  <q-item-section>
                    <q-item-label v-html="child.label" class="q-ml-md" ></q-item-label>
                  </q-item-section>
                </q-item>
              </template>
            </q-expansion-item>
          </template>
        </q-select>
      </div>
    </div>
</div>
!

CSS
!

JS 

              
                new Vue({
  el: '#q-app',
  data () {
    return {
      model: null,
      options: [
        {
          label: 'American cars',
          children: [
            {
              label: 'Ford'
            },
            {
              label: 'General Motors'
            },
            {
              label: 'Tesla'
            }
          ]
        },
        {
          label: 'German cars',
          children: [
            {
              label: 'Audi'
            },
            {
              label: 'BMW'
            },
            {
              label: 'Porsche'
            }
          ]
        },
        {
          label: 'Italian cars',
          children: [
            {
              label: 'Ferrari'
            },
            {
              label: 'Lamborghini'
            },
            {
              label: 'Maserati'
            }
          ]
        },
        {
          label: 'Japanese cars',
          children: [
            {
              label: 'Honda'
            },
            {
              label: 'Nissan'
            },
            {
              label: 'Toyota'
            }
          ]
        },
        {
          label: 'Option without children',
          children: [
          ]
        }
      ]
    }
  },

  methods: {
    getLabel (scope) {
      debugger
      console.log(scope)
      return scope.label
    },
    hasChild (scope) {
      return scope.opt.children.some(c => c.label === this.model)
    }
  }
})
!
999px

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