{
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      "name": "a"
    },
    {
      "name": "b"
    },
    {
      "name": "a1"
    },
    {
      "name": "a2"
    },
    {
      "name": "b1"
    },
    {
      "name": "b2"
    }
  ],
  "links": [
    {
      "source": "a",
      "target": "a1",
      "value": "@integer(0, 10)"
    },
    {
      "source": "a",
      "target": "a2",
      "value": "@integer(0, 10)"
    },
    {
      "source": "b",
      "target": "b1",
      "value": "@integer(0, 10)"
    },
    {
      "source": "a",
      "target": "b1",
      "value": "@integer(0, 10)"
    },
    {
      "source": "b1",
      "target": "a1",
      "value": "@integer(0, 10)"
    },
    {
      "source": "b1",
      "target": "b2",
      "value": "@integer(0, 10)"
    }
  ],
  "levels": [
    {
      "depth": 0,
      "itemStyle": {
        "color": "#decbe4"
      },
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        "color": "source",
        "opacity": 0.9
      }
    },
    {
      "depth": 1,
      "itemStyle": {
        "color": "#b3cde3"
      },
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    {
      "depth": 2,
      "itemStyle": {
        "color": "#ccebc5"
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}