# Pyth, 9 bytes

    j.e+*dkbG

[Try it online][1]

### Explanation

     .e     G  For each element of 'abc...z'...
        *dk    Take a string of spaces with length equal to the index...
       +   b   Add the letter...
    j          Join the results with newlines.

  [1]: https://pyth.herokuapp.com/?code=j.e%2B%2AdkbG&debug=0