Angular TreeGrid (ej2 syncfusion) connection with backend API data not rendered

Question

Does anybody use ej2 syncfusion angular UI components? I am trying to connect my backend API with their TreeGrid component, The connection works fine, the request gives data successfully, but the TreeGrid isn't rendered any data from BE side. Here are my code examples; in component:

        this.tableData = new DataManager({
        url: `http://localhost:3000/table-data/? 
        &dataId=${this.storageService.getTableDataId()}`, adaptor: new  
        WebApiAdaptor, 
        crossDomain: true })

in view:

<ng-container  *ngIf="tableData">
  <ejs-treegrid #treegrid [dataSource]='tableData'
                height='100vh'
                [pageSettings]="{pageSize: 30, pageCount: 1}"
                [enableInfiniteScrolling]="true"
                (actionBegin)="getNewPage($event)"
                [treeColumnIndex]='1'
                allowPaging='false'>

      <e-columns>
          <e-column
            field='serialNumber'
            headerText='serialNumber'
            width='120'
            textAlign='Center'>
          </e-column>
          <e-column
            field='description'
            headerText='description'
            width='50'>
          </e-column>
          <e-column
            field='companyName'
            headerText='companyName'
            width='50'>
          </e-column>
          <e-column
            field='employeeName'
            headerText='employeeName'
            width='100'>
          </e-column>
        </e-columns>
      </ejs-treegrid>
    </ng-container>

data what I send from BE:

{
count: number;
dataId: string:
rows: object[];
}