Semi-Diagonal Alphabet Given a letter of the English alphabet, your task is to build a semi-diagonal alphabet to the input. 

How to build a Semi-Diagonal alphabet?

Brief Description: 
First, you take the position of the letter in the alphabet, P (P is 1-indexed here). Then, you print each letter until the input (inclusive) on a line, preceded by P-1 and repeat that letter P times, interleaving with spaces.

Examples: 


Given F, your program should output:


A 
 B B 
  C C C 
   D D D D 
    E E E E E 
     F F F F F F 

Given K, your program should output:


A
 B B 
  C C C 
   D D D D 
    E E E E E 
     F F F F F F 
      G G G G G G G 
       H H H H H H H H 
        I I I I I I I I I 
         J J J J J J J J J J 
          K K K K K K K K K K K 

Given A, your program should output:

A



Rules


You may choose either lowercase or uppercase characters, but that should be consistent.
You may have extraneous spaces as follows:


One consistent leading space (on each line).
A trailing or leading newline(s).
Trailing spaces.

Input and output can be taken by any standard mean, and default loopholes apply.
You are allowed to output a list of lines instead, as long as you also provide the ascii-art version.
This is code-golf, so the shortest code in bytes wins!


Inspired by this challenge.
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)