5 [Edit removed during grace period]
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4 added 45 characters in body
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Python 2, 63 6161 59 bytes

-2 bytes thanks to Rod. -2 bytes thanks to Felipe Nardi Batista.

i=0i=1
exec"print' '*i+'%c '%(i+65i+64)*-~i;i+=1;"**i;i+=1;"*(ord(input())-64)

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Python 2, 63 61 bytes

-2 bytes thanks to Rod.

i=0
exec"print' '*i+'%c '%(i+65)*-~i;i+=1;"*(ord(input())-64)

Try it online!

Python 2, 63 61 59 bytes

-2 bytes thanks to Rod. -2 bytes thanks to Felipe Nardi Batista.

i=1
exec"print' '*i+'%c '%(i+64)*i;i+=1;"*(ord(input())-64)

Try it online!

3 added 34 characters in body
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Python 2, 6363 61 bytes

-2 bytes thanks to Rod.

i=0
exec"print' '*i+('%c'*i+'%c '%(i+65))*-~i;i+=1;"*(ord(input())-64)

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Python 2, 63 bytes

i=0
exec"print' '*i+('%c '%(i+65))*-~i;i+=1;"*(ord(input())-64)

Try it online!

Python 2, 63 61 bytes

-2 bytes thanks to Rod.

i=0
exec"print' '*i+'%c '%(i+65)*-~i;i+=1;"*(ord(input())-64)

Try it online!

2 deleted 24 characters in body
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1
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