1 for l=0 to 13:read s
2 for n=-s to s:poke 1043+n+40*l,42
3 nextn:nextl
4 data 0,1,2,3,1,3,5,7,2,5,8,11,1,1
ready.
Install vice, drag and drop the prg file into it
l is the number of the line of the christmas tree (0 is the top row)
2s+1 is the number of "*" in a line.
This program uses also the poke 1043+n+40*l,42 who puts star "*" at the line number l and at the column number n
after the column center (on the right if n is positive and on the left if n is negative)