Tree transformations in VegaJS

Is it possible, especially in Vega 3, to do tree visualizations if the resulting data is already in a "tree-like" form? Generalized - is it possible to transform/draw a tree, if there are a few extra objects/lists wrapping each sublevel? Each sublevel would have an identical substructure. Ideally, I want to specify an expression for the subtree key (relative to current), and the list of subelements (also relative to current).

{
  "responses": [
    {
      ...
      "aggregations": {
        "sublevel": {
          "buckets": [
            {
              "key": "MA",
              "sublevel": {
                "buckets": [
                  {
                    "key": "Fivepointville",
                    "sum": { "value": 48249.0 }
                  },
                  {
                    "key": "Makena",
                    "sum": { "value": 46010.0 }
                  },
                  ...
                ]
              },
              "sum": { "value": 624256.0 }
            },
            {
              "key": "TX",
              "sublevel": {
                "buckets": [
                  {
                    "key": "Craig",
                    "sum": { "value": 49587.0 }
                  },
                  {
                    "key": "Driftwood",
                    "sum": { "value": 43219.0 }
                  }