Perl - 55 characters with say:

say ' 'x($N-$_).'* 'x$_ for 1..$N;say ' 'x($N-2).'| |';

My JavaScript solution - 82 103 chars:

a=n=>{for(s=‘’,i=1;i<=n;i++)s+=’ ‘.repeat(n-i)+’* ‘.repeat(i)+’\n’;console.log(s)}

a=n=>{for(s='',i=0;++i<=n;)s+=' '.repeat(n-i)+'* '.repeat(i)+'\n';console.log(s+' '.repeat(n-2)+'| |')}

I’m happy I was able to beat ChatGPT, it had the same strategy but used additional for loops instead of string.repeat(), so it was 113 chars. But I suspect further improvements might be possible with array.reduce or other prototype functions I’m forgetting about.

Python - 94 chars

I tried using some alternatives, but they all ended up more verbose than:

def a(n):
 for i in range(0,n):
  print(' '*(n-i)+'* '*(i+1)+' '*(n-i-1))
 print(' '*(n-1)+'| |')

The list tools in python are great, but they all use keywords, so doing anything that doesn’t directly do for and print is likely too much. You could make a list of strings for instance, and print it all out at once to save a ‘print’ but you’d end up using a for in list comprehension or a join or something, so you can’t really save any characters afaict.

I’m sure someone will find a way to beat it tho!

Just discovered this community existed, I’ve got to make a post in my usual golfing lang:

Zsh, 70 bytes

l=()
repeat $1 l=(${(l.++i.)}\* $^l' *')
print -l $l ${(l.$1-1.)}'| |'

Try it online!

The key constructs here are (l.ARITHMETIC EXPRESSION.), which left-pads, and $^l, which expands the array like a cross product. a=(a b c); echo x$a prints xa b c, but echo x$^a prints xa xb xc.

Interestingly, print -l was shorter than <<< by one byte.

I don’t know about how y’all feel about submissions in dedicated golfing languages/esolangs like this, but

Vyxal - 14 characters/SBCS bytes (22 UTF-8 bytes)

ɾ×*vṄ| |JøĊ⁋

Vyxal is a stack-based esolang designed to do well in code-golf competitions just like this one. It’s far from the only golfing language in existence, there’s many more like 05AB1E, Jelly and Thunno 2. This one is just one I made in 2020 (yes creative naming I know, I just couldn’t think of anything better).

You can try the program online here

Explained:

ɾ×*vṄ`| |`JøĊ⁋
ɾ               # Generate a list of numbers from 1 to the input.
 ×*             # Repeat the character "*" n many times, for each n in the above list
   vṄ           # Insert a space between each asterisk. Normally, Ṅ will join an entire list on spaces, but the v makes Ṅ apply to each item in a list.
     `| |`J     # Append the string "| |" to that list - this is the stump of the tree
           øĊ   # Centre each of the strings in the list, relative to the longest string in the list. This is a single built-in function (the ø indicates that it's a two-character function)
             ⁋  # Join the resulting list on newlines

For input = 5, the stack looks like so:

ɾ×*vṄ`| |`JøĊ⁋
ɾ                [1, 2, 3, 4, 5]
 ×*              ["*", "**", "***", "****", "*****"] (* does the multiplication, the × is the character that pushes "*" to the stack - it was a later addition)
   vṄ            ["*", "* *", "* * *", "* * * *", "* * * * *"]
     `| |`J      ["*", "* *", "* * *", "* * * *", "* * * * *", "| |"]
           øĊ    ["    *    ", "   * *   ", "  * * *  ", " * * * * ", "* * * * *", "   | |   "]
             ⁋   Output as in the original challenge post

As you can see, some built-ins automatically apply to each item in a list, as if you wrote [f(x) for x in iterable].

Once again, I don’t mean to come in and ruin golf for everyone, I just want to see how such a language might be seen by the community.

Here’s my attempt with Rust:

101 Characters:

fn a(n:usize){for i in 1..=n{println!("{:2$}{}","","* ".repeat(i),n-i);}println!("{:1$}| |","",n-2);}

Rust Playground Link

(Edited to remove a few unnecessary whitespace characters)

JavaScript, 93 characters:

l=console.log,r='repeat',b=n=>{for(i=0;i++<n;l(' '[r](n-i)+'* '[r](i)));l(' '[r](n-2)+'| |')}