Shel Silverstein: A Boy Named Sue and The Giving Tree

I did not realize that poet Shel Silverstein wrote Johnny Cash's classic tune "A Boy Named Sue."  Watch this clip from The Johnny Cash Show in the late 1960's:  https://www.youtube.com/watch?v=7e5ZVIpB4sw.

Some animations of his poems can be found here:  http://www.shelsilverstein.com/books/#animations
In addition, his site has some excellent resources for educators.

One of his most famous poems is called "The Giving Tree."  You can hear him read his poem from a 1973 film:  https://www.youtube.com/watch?v=1TZCP6OqRlE.  There are many opinions about how to interpret the relationship between the tree and the boy.  Some believe it represents a parent-child relationship while others see religious significance to the relationship.  What do you think?