split tree.md into linux and osx versions, to cater to the different sets of available options

pages/linux/tree.md

@@ -0,0 +1,27 @@
+# tree
+
+> Show the contents of the current directory as a tree.
+
+- Show files and directories up to 'num' levels of depth (where 1 means the current directory):
+
+`tree -L {{num}}`
+
+- Show directories only:
+
+`tree -d`
+
+- Show hidden files too:
+
+`tree -a`
+
+- Print the tree without indentation lines, showing the full path instead:
+
+`tree -i -f`
+
+- Print the size of each node next to it, in human-readable format:
+
+`tree -s -h`
+
+- Filter the tree using a wildcard (glob) pattern:
+
+`tree -P {{*.txt}}`