Why does 'tree' command ignore directories but not files

Question

tree shows

...
│  ├── template_one_file.sh
│  ├── template_sed.sh
│  ├── testy.sh
│  ├── tmp
│  │  ├── file1.html.13567_old
│  │  ├── file2.html.13567_old
│  │  ├── file3.html.13567_old
│  │  └── file4.html.13567_old
│  └── use_case_to_add_etc_2_numbers
└── vi
 ├── vim_tips_and_chearsheet
 └── vi_stuff
160 directories, 713 files

and I can ignore the tmp directory (for example) with tree -I 'tmp' -L 4

...
│  ├── template_multiple_files.sh
│  ├── template_one_file.sh
│  ├── template_sed.sh
│  ├── testy.sh
│  └── use_case_to_add_etc_2_numbers
└── vi
 ├── vim_tips_and_chearsheet
 └── vi_stuff
157 directories, 709 files

but why can I not ignore individual files such as the _old files with

tree -I 'old' -L 4

which still shows the _old files

...
│  ├── template_multiple_files.sh
│  ├── template_one_file.sh
│  ├── template_sed.sh
│  ├── testy.sh
│  ├── tmp
│  │  ├── file1.html.13567_old
│  │  ├── file2.html.13567_old
│  │  ├── file3.html.13567_old
│  │  └── file4.html.13567_old
│  └── use_case_to_add_etc_2_numbers
└── vi
 ├── vim_tips_and_chearsheet
 └── vi_stuff
160 directories, 713 files

I tried '.*old' and '.*old$' patterns but that didn't help.

• Munir: Use shell glob patterns, not regex.

Answer 1

Use a wildcard:

tree -I '*_old' -L 4

Reference: man tree (my emphasis)

-I pattern

Do not list those files that match the wild-card pattern.