tree command is not instaled by default. I don't know how to install it in android via terminal but you could allways use the ls command, but yes it doesn't show you a tree format that it is easy to understand, but still does the job.
ls -d */
Only list the directories in the current directory.
List all files by the time they were last modified in reverse order. In other words the last files listed are the most recently modified files.
I will try and find a way to install the tree package. If i find something I will let you know.
Also install busybox to have more unix command avaible. Reference