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.
ls -ltr
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