Treemap

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      {"id":4,"name":"Physics","parent":1,"size":null},
      {"id":5,"name":"Genetics","parent":2,"size":40},
      {"id":6,"name":"Ecology","parent":2,"size":25},
      {"id":7,"name":"Organic","parent":3,"size":35},
      {"id":8,"name":"Inorganic","parent":3,"size":15},
      {"id":9,"name":"Quantum","parent":4,"size":30},
      {"id":10,"name":"Mechanics","parent":4,"size":20}
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    "transform":[{"type":"stratify","key":"id","parentKey":"parent"},
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  "scales":[{"name":"color","type":"ordinal","range":{"scheme":"category10"},"domain":{"data":"tree","field":"name"}}],
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