I am sad to say that the tree command does not exist for RHEL4, nor is it intended for it.
(See this link)
Lucky for me there is a (very long) command that can simulate it.
Go to the folder whose tree you need, and type this :
# ls -R | grep “:$” | sed -e ‘s/:$//’ -e ‘s/[^-][^\/]*\//–/g’ -e ‘s/^/ /’ -e ‘s/-/|/’
Output is quite OK, not exectly tree-like, but it will do…..