Python 3, 61 bytes

lambda l:[' '*i+-~i*(chr(i+65)+' ')for i in range(ord(l)-64)]

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Python 3, 59 bytes

lambda l:[' '*i+'%c '%(i+65)*-~i for i in range(ord(l)-64)]

Try it online!

Python 3 , 61 bytes

lambda l:[' '*i+-~i*(chr(i+65)+' ')for i in range(ord(l)-64)]

Try it online! (link to pretty-print version)