Need to convert columns to rows

Question

I have data that looks like

a  b  c
1  4  7
2  5  8
3  6  9

I want to convert it to convert all the columns to rows and want an output like this

type value
a      1
a      2
a      3
b      4
b      5
b      6
c      7
c      8
c      9

i have no idea do this help