tree支持通配符，用tree可以快速显示项目下的源码文件目录结构，如：
tree -L 6 -P "*.c"
tree - list contents of directories in a tree-like format.
-L level
Max display depth of the directory tree.
-P pattern
List only those files that match the wild-card pattern. Note: you must use the -a option to also consider those files beginning with a dot `.' for matching. Valid wildcard operators are `*' (any zero or more charac‐
ters), `?' (any single character), `[...]' (any single character listed between brackets (optional - (dash) for character range may be used: ex: [A-Z]), and `[^...]' (any single character not listed in brackets) and
`|' separates alternate patterns.
