A golfed version for a sig... the major improvement IMHO being the symbol function.

sub c{rand>.07&&return'*';rand>.5?'o':'|';}my$w=shift()/2||15;for my$i
+(1..$w)
{print"\n",' 'x($w-$i);print c for 1..2*$i;}print"\n",' 'x($w-2),"_||_
+\n\n\n";
[download]

I couldn't come up with a decent star to top the tree...