how do i setup multiple columns into a single row and expand later

[prakash]

in a first column i give a order no "a" and in the second column i type "2"
"3" and "4" one belowthe other.
In the fourth row of the first column I type "b" and type "5" in the next
column.
The format would be like this

a 2
3
4
b 5
What i need is i want to freeze the "a" to a single row like
a 2
b 5
and later expand which should bring to the older format