Use find to list the current folder:

find . -print | sed -e 's;[^/]*/;|____;g;s;____|; |;g'

Add to ~/.bash_profile or ~/.zshrc
alias tree="find . -print | sed -e 's;[^/]*/;|____;g;s;____|; |;g'"
　　

Or install the tree with brew
brew install tree