public void CompoundOperation(Autodesk.Revit.DB.Document document)
{
   // All and any transaction group should be enclosed in a 'using' block or guarded within 
   // a try-catch-finally blocks to guarantee that the group does not out-live its scope.
   using (TransactionGroup transGroup = new TransactionGroup(document, "Level and Grid"))
    {
       if (transGroup.Start() == TransactionStatus.Started)
       {
          // We are going to call two methods, each having its own local transaction.
          // For our compound operation to be considered successful, both the individual
          // transactions must succeed. If either one fails, we will roll our group back,
          // regardless of what transactions might have already been committed.

          if (CreateLevel(document, 25.0) && CreateGrid(document, new XYZ(0,0,0), new XYZ(10,0,0)))
          {
             // The process of assimilating will merge the two (or any number of) committed
             // transaction together and will assign the grid's name to the one resulting transaction,
             // which will become the only item from this compound operation appearing in the undo menu.
             transGroup.Assimilate();
          }
          else
          {
             // Since we could not successfully finish at least one of the individual
             // operation, we are going to roll the entire group back, which will
             // undo any transaction already committed while this group was open.
             transGroup.RollBack();
          }
       }
    }
}

Public Sub CompoundOperation(document As Autodesk.Revit.DB.Document)
    ' All and any transaction group should be enclosed in a 'using' block or guarded within 
    ' a try-catch-finally blocks to guarantee that the group does not out-live its scope.
    Using transGroup As New TransactionGroup(document, "Level and Grid")
        If transGroup.Start() = TransactionStatus.Started Then
            ' We are going to call two methods, each having its own local transaction.
            ' For our compound operation to be considered successful, both the individual
            ' transactions must succeed. If either one fails, we will roll our group back,
            ' regardless of what transactions might have already been committed.


            If CreateLevel(document, 25.0) AndAlso CreateGrid(document, New XYZ(0, 0, 0), New XYZ(10, 0, 0)) Then
                ' The process of assimilating will merge the two (or any number of) committed
                ' transaction together and will assign the grid's name to the one resulting transaction,
                ' which will become the only item from this compound operation appearing in the undo menu.
                transGroup.Assimilate()
            Else
                ' Since we could not successfully finish at least one of the individual
                ' operation, we are going to roll the entire group back, which will
                ' undo any transaction already committed while this group was open.
                transGroup.RollBack()
            End If
        End If
    End Using
End Sub