05AB1E, 15 14 13 bytes

Saved 1 byte thanks to Adnan

A¹¡н«ƶ€S»¶¡āú» 

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Explanation

A # push lowercase alphabet ¹¡ # split at input н # get the first part « # append the input ƶ # repeat each a number of times corresponding to its 1-based index €S # split each to a list of chars » # join on spaces and newlines ¶¡ # split on newlines āú # prepend spaces to each corresponding to its 1-based index » # join on newlines 

05AB1E, 15 14 13 bytes

Saved 1 byte thanks to Adnan

A¹¡н«ƶ€S»¶¡āú» 

Try it online! or the Ascii art version

Explanation

A # push lowercase alphabet ¹¡ # split at input н # get the first part « # append the input ƶ # repeat each a number of times corresponding to its 1-based index €S # split each to a list of chars » # join on spaces and newlines ¶¡ # split on newlines āú # prepend spaces to each corresponding to its 1-based index » # join on newlines 

05AB1E, 15 14 bytes

ADIk>£ƶ€S»¶¡āú» 

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Explanation

AD # push 2 copies of the alphabet   Ik # get the index of the input in the alphabet   > # increment  £ # take this many characters from the alphabet   ƶ # repeat each a number of times corresponding to its 1-based index   €S # split each to a list of chars   » # join on spaces and newlines   ¶¡ # split on newlines   āú # prepend spaces to each corresponding to its 1-based index   » # join on newlines 

05AB1E, 15 14 13 bytes

Saved 1 byte thanks to Adnan

A¹¡н«ƶ€S»¶¡āú» 

Try it online! or the Ascii art version

Explanation

A # push lowercase alphabet ¹¡ # split at input н # get the first part  « # append the input ƶ # repeat each a number of times corresponding to its 1-based index €S # split each to a list of chars » # join on spaces and newlines ¶¡ # split on newlines āú # prepend spaces to each corresponding to its 1-based index » # join on newlines 

05AB1E, 15 bytes

ADIk>£ƶvySðýNú, 

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Explanation

AD # push 2 copies of the lowercase alphabet Ik # get the index of the input in the alphabet > # increment £ # take that many elements ƶ # multiply each element by its index v # for each element in the resulting list yS # split it to a list of chars ðý # join by spaces Nú # prepend N spaces where N is the elements index in the list , # print with newline 

05AB1E, 15 14 bytes

ADIk>£ƶ€S»¶¡āú» 

Try it online! or the Ascii art version

Explanation

AD  # push 2 copies of the alphabet Ik  # get the index of the input in the alphabet >  # increment £  # take this many characters from the alphabet ƶ  # repeat each a number of times corresponding to its 1-based index €S # split each to a list of chars » # join on spaces and newlines ¶¡  # split on newlines āú  # prepend spaces to each corresponding to its 1-based index »  # join on newlines