var
  MasterNode: PVirtualNode;
  DetailNode: PVirtualNode;
begin
  // move both table cursors to the beginning
  MasterTable.First;
  DetailTable.First;
  // clear and lock the virtual tree
  VirtualTree.Clear;
  VirtualTree.BeginUpdate;
  try
    // iterate the master table in the outer loop
    while not MasterTable.Eof do
    begin
      // add the master table row as the root node
      MasterNode := VirtualTree.AddChild(nil);
      // <- fill in the data for the MasterNode here
      // while we are not at the end of the detail table and the detail row is of the same ID as the master,
      // add child nodes
      while not DetailTable.Eof and (DetailTable.FieldByName('MasterID') = MasterTable.FieldByName('ID')) do
      begin
        // add a detail node as a child of the parent node added for the master table
        DetailNode := VirtualTree.AddChild(MasterNode);
        // <- fill in the data for the DetailNode here
        // move to the next detail row
        DetailTable.Next;
      end;
      // move to the next master row
      MasterTable.Next;
    end;
  finally
    VirtualTree.EndUpdate;
  end;
end;