Please use the following code snippet to setup the Gantt view:
Sub New()
InitializeComponent()
Dim dt As New DataTable
dt.Columns.Add("ID", GetType(Integer))
dt.Columns.Add("Group_ID", GetType(Integer))
dt.Columns.Add("Title", GetType(String))
dt.Columns.Add("Start", GetType(DateTime))
dt.Columns.Add("End", GetType(DateTime))
dt.Rows.Add(-999, 0, "Root", New DateTime(2019, 8, 21), New DateTime(2019, 8, 30))
dt.Rows.Add(6, -999, "Item 1", New DateTime(2019, 8, 21), New DateTime(2019, 8, 23))
dt.Rows.Add(7, -999, "Item 2", New DateTime(2019, 8, 26), New DateTime(2019, 8, 30))
dt.Rows.Add(1000, 6, "Sub1.1", New DateTime(2019, 8, 21), New DateTime(2019, 8, 22))
dt.Rows.Add(1001, 6, "Sub1.2", New DateTime(2019, 8, 22), New DateTime(2019, 8, 23))
dt.Rows.Add(1002, 6, "Sub1.3", New DateTime(2019, 8, 23), New DateTime(2019, 8, 23))
dt.Rows.Add(1003, 7, "Sub2.1", New DateTime(2019, 8, 26), New DateTime(2019, 8, 29))
Me.RadGanttView1.DataSource = dt
Me.RadGanttView1.ChildMember = "ID"
Me.RadGanttView1.ParentMember = "Group_ID"
Me.RadGanttView1.TitleMember = "Title"
Me.RadGanttView1.StartMember = "Start"
Me.RadGanttView1.EndMember = "End"
Me.RadGanttView1.Columns.Add("ID")
Me.RadGanttView1.Columns.Add("Title")
Me.RadGanttView1.GanttViewElement.GraphicalViewElement.TimelineStart = New DateTime(2019, 8, 20)
End Sub
However, if you switch the order of adding the rows, not all items will be visible in RadGanttView:
dt.Rows.Add(1000, 6, "Sub1.1", New DateTime(2019, 8, 21), New DateTime(2019, 8, 22))
dt.Rows.Add(1001, 6, "Sub1.2", New DateTime(2019, 8, 22), New DateTime(2019, 8, 23))
dt.Rows.Add(1002, 6, "Sub1.3", New DateTime(2019, 8, 23), New DateTime(2019, 8, 23))
dt.Rows.Add(1003, 7, "Sub2.1", New DateTime(2019, 8, 26), New DateTime(2019, 8, 29))
dt.Rows.Add(6, -999, "Item 1", New DateTime(2019, 8, 21), New DateTime(2019, 8, 23))
dt.Rows.Add(7, -999, "Item 2", New DateTime(2019, 8, 26), New DateTime(2019, 8, 30))