The i3wm-save.sh script saves the workspaces N (1-10) to a json file. The i3wm-load.sh script loads that configuration into i3wm.
Note that these json files need further editing according to the i3wm documentation: https://i3wm.org/docs/layout-saving.html
For easier reloading of the layout you can add something like that to your i3 config:
# restore workspace layout
bindsym $mod+g exec ~/i3wm-load.sh
For beeing able to run "i3-save-tree" you need to install "perl-anyevent-i3": https://www.archlinux.org/packages/?name=perl-anyevent-i3