If your data items contain collections of child items, you may use the FlexGrid's childItemsPath to show the data as a tree.
For example, consider a list of 'person' objects which have a 'children' property. The 'children' property contains an array of more person objects. This is sometimes called a homogeneous hierarchy.
The grid below was built by binding the grid to the top-level persons list and setting the childItemsPath property to 'children':