Edit in JSFiddle

const dataSource = {
  "chart": {
    "caption": "New Store Opening - Project Plan",
    "dateformat": "dd/mm/yyyy",
    "outputdateformat": "ddds mns yy",
    "ganttwidthpercent": "60",
    "ganttpaneduration": "40",
    "ganttpanedurationunit": "d",
    "useverticalscrolling": "0",
    "plottooltext": "<b>$label</b><br>Start: <b>$start</b><br>End: <b>$end</b>",
    "theme": "fusion"
  },
  "connectors": [
    {
      "connector": [
        {
          "fromtaskid": "1-1",
          "totaskid": "2-1",
          "color": "#F2726F",
          "thickness": "2"
        },
        {
          "fromtaskid": "2-1",
          "totaskid": "3-1",
          "color": "#F2726F",
          "thickness": "2"
        },
        {
          "fromtaskid": "3-1",
          "totaskid": "4-1",
          "color": "#F2726F",
          "thickness": "2"
        },
        {
          "fromtaskid": "4-1",
          "totaskid": "5-1",
          "color": "#F2726F",
          "thickness": "2"
        },
        {
          "fromtaskid": "5-1",
          "totaskid": "6-1",
          "color": "#F2726F",
          "thickness": "2"
        },
        {
          "fromtaskid": "6-1",
          "totaskid": "7-1",
          "color": "#F2726F",
          "thickness": "2"
        },
        {
          "fromtaskid": "7-1",
          "totaskid": "8-1",
          "color": "#F2726F",
          "thickness": "2"
        },
        {
          "fromtaskid": "8-1",
          "totaskid": "9-1",
          "color": "#F2726F",
          "thickness": "2"
        },
        {
          "fromtaskid": "9-1",
          "totaskid": "10-1",
          "color": "#F2726F",
          "thickness": "2"
        }
      ]
    }
  ],
  "trendlines": [
    {
      "line": [
        {
          "start": "14/4/2018",
          "displayvalue": "AC Testing",
          "color": "5D5D5D",
          "thickness": "1",
          "dashed": "1"
        }
      ]
    }
  ],
  "milestones": {
    "milestone": [
      {
        "date": "30/4/2018",
        "taskid": "10-1",
        "color": "#f8bd19",
        "shape": "star",
        "tooltext": "Store Opening"
      }
    ]
  },
  "tasks": {
    "task": [
      {
        "label": "Clear Site (4 Days)",
        "processid": "1",
        "start": "1/3/2018",
        "end": "5/3/2018",
        "id": "1-1",
        "color": "#5D62B5"
      },
      {
        "label": "Drainage & Foundation (7 Days)",
        "processid": "2",
        "start": "6/3/2018",
        "end": "13/3/2018",
        "id": "2-1",
        "color": "#5D62B5"
      },
      {
        "label": "Ground Floor (8 Days)",
        "processid": "3",
        "start": "14/3/2018",
        "end": "22/3/2018",
        "id": "3-1",
        "color": "#5D62B5"
      },
      {
        "label": "First Floor (5 Days)",
        "processid": "4",
        "start": "23/3/2018",
        "end": "28/3/2018",
        "id": "4-1",
        "color": "#5D62B5"
      },
      {
        "label": "Roofing (5 Days)",
        "processid": "5",
        "start": "29/3/2018",
        "end": "3/4/2018",
        "id": "5-1",
        "color": "#5D62B5"
      },
      {
        "label": "Connect Electricity (6 Days)",
        "processid": "6",
        "start": "4/4/2018",
        "end": "10/4/2018",
        "id": "6-1",
        "color": "#5D62B5"
      },
      {
        "label": "Air Conditioning (3 Days)",
        "processid": "7",
        "start": "11/4/2018",
        "end": "14/4/2018",
        "id": "7-1",
        "color": "#5D62B5"
      },
      {
        "label": "Interiors (8 Days)",
        "processid": "8",
        "start": "15/4/2018",
        "end": "23/4/2018",
        "id": "8-1",
        "color": "#5D62B5"
      },
      {
        "label": "Racking (3 Days)",
        "processid": "9",
        "start": "24/4/2018",
        "end": "28/4/2018",
        "id": "9-1",
        "color": "#5D62B5"
      },
      {
        "label": "Stock Shelving (1 Days)",
        "processid": "10",
        "start": "29/4/2018",
        "end": "30/4/2018",
        "id": "10-1",
        "color": "#5D62B5",
        "toppadding": "9"
      }
    ]
  },
  "processes": {
    "headertext": "Task",
    "isanimated": "1",
    "headervalign": "bottom",
    "headeralign": "left",
    "align": "left",
    "isbold": "1",
    "bgalpha": "25",
    "process": [
      {
        "label": "Clear site",
        "id": "1"
      },
      {
        "label": "Drainage & Foundation",
        "id": "2"
      },
      {
        "label": "Ground Floor",
        "id": "3"
      },
      {
        "label": "First Floor",
        "id": "4"
      },
      {
        "label": "Roofing",
        "id": "5"
      },
      {
        "label": "Connect Electricity",
        "id": "6"
      },
      {
        "label": "Air Conditioning",
        "id": "7"
      },
      {
        "label": "Interiors",
        "id": "8"
      },
      {
        "label": "Racking",
        "id": "9"
      },
      {
        "label": "Stock Shelving",
        "id": "10"
      }
    ]
  },
  "categories": [
    {
      "align": "middle",
      "category": [
        {
          "start": "1/3/2018",
          "end": "31/3/2018",
          "label": "March"
        },
        {
          "start": "1/4/2018",
          "end": "1/5/2018",
          "label": "April"
        }
      ]
    },
    {
      "align": "center",
      "category": [
        {
          "start": "1/3/2018",
          "end": "7/3/2018",
          "label": "Week 1"
        },
        {
          "start": "8/3/2018",
          "end": "14/3/2018",
          "label": "Week 2"
        },
        {
          "start": "15/3/2018",
          "end": "21/3/2018",
          "label": "Week 3"
        },
        {
          "start": "22/3/2018",
          "end": "28/3/2018",
          "label": "Week 4"
        },
        {
          "start": "29/3/2018",
          "end": "5/4/2018",
          "label": "Week 5"
        },
        {
          "start": "6/4/2018",
          "end": "12/4/2018",
          "label": "Week 6"
        },
        {
          "start": "13/4/2018",
          "end": "19/4/2018",
          "label": "Week 7"
        },
        {
          "start": "19/4/2018",
          "end": "25/4/2018",
          "label": "Week 8"
        },
        {
          "start": "25/4/2018",
          "end": "1/5/2018",
          "label": "Week 9"
        }
      ]
    }
  ]
};

FusionCharts.ready(function() {
   var myChart = new FusionCharts({
      type: "gantt",
      renderAt: "chart-container",
      width: "800",
      height: "500",
      dataFormat: "json",
      dataSource
   }).render();
});
<div id="chart-container"></div>