How can I get backlog wise task ?

See more:

C#

.NET

TFS

VS-Online

Now I can get all the task through getting work item.

WorkItemStore workItemStore = teamProjectCollection.GetService<WorkItemStore>();
                     string projectName = dr["ProjectName"].ToString();

                     DateTime max = commonSvc.getMaxDate(groupId, accountName, projectName).Date;

                     WorkItemCollection workItemCollection = workItemStore.Query(
                     " SELECT * " +
                     " FROM WorkItems " +
                     " WHERE [System.TeamProject] = '" + projectName + "'  ORDER BY [System.WorkItemType], [System.Id]");

Then I can categories them by workItem type (like epic,bug, task) etc.

Now I want get task item hierarchically. I want get the backlog list then for each back I want to get tasklist. This will be looking like

1. Get a list backlog item. Then

 foreach (Backlog backlog in BacklogList)
{
   GetTaskListForThisBacklog(backlog );
}

Please help me to find out task item hierarchically.