Haskell, (削除) 52 (削除ここまで) 44 bytes
f k=[[" ",s:" "]>>=(['A'..s]>>)|s<-['A'..k]]
Returns a list of lines.
f k= -- main function is f, input parameter k
[ |s<-['A'..k]] -- for each s from ['A'..k]
>>= -- map (and collect the results in a single string) the function:
(['A'..s]>>) -- replace each element in ['A'..s] with
[ , ] -- over the list, containing
" " -- a single space to get the indent
s:" " -- s followed by space to get the letter sequence
Edit: @jferard: saved three bytes. Thanks!
nimi
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