test.json

{
  "nodes": [
    { "id": "com1" , "sequence":0, "fixed": true, "x":100,"y":100 },
    { "id": "com2" , "sequence":1, "fixed": true, "x":100,"y":100 },
    { "id": "com3" , "sequence":1, "fixed": true, "x":100,"y":100 },
    { "id": "com4" , "sequence":2, "fixed": true, "x":100,"y":100 },
    { "id": "com5" , "sequence":2, "fixed": true, "x":100,"y":100 },
    { "id": "com6" , "sequence":2, "fixed": true, "x":100,"y":100 }
  ],
  "links": [
    { "source":"com1","target":"com2" },
    { "source":"com1","target":"com3" },
    { "source":"com2","target":"com4" },
    { "source":"com3","target":"com5" },
    { "source":"com3","target":"com6" }
  ]  
}