Merging two tables

I have got my dataset DS_A. I have got my dataset DS_B.
I read table_A into DS_A from an Excel file.
I read table_B into DS_B from an Excel file.

Now I want to view these two tables together in one datagrid.

I have found the DS_A.merge command, but it keeps merging my DS_A with whatever I send to it, instead of merging what I send to it with table_A in DS_A.

The following:
DS_A.Merge(DS_B.Tables(0), False, MissingSchemaAction.Add)
or
DS_A.Merge(DS_B, False, MissingSchemaAction.Add)

Results in DS_A getting another table, while I want DS_A to contain just my table_A while all data from table_B has been added.

How could I get what I want?