Actually, the "tree" is a pile of rocks at the top of a hill right along Highway 85.  When my grandpa was a kid, he used to pile up rocks on high points and my dad and his sister and cousins continued doing so.  This is the only one visible from the highway though.  If you've ever driven between the Watford City/Belfield area on that route, you've most likely seen the rock pile.  For an idea of how high the rocks are, my son is 3 1/2 feet tall in the picture.   
 
On the 4th of July every year since I was a baby, my dad would tie a US flag (on a flagpole) around the rock and it would wave proudly throughout the day.  I remember as a youngster waking up early on the 4th every year so I could make my way out to the hill with him and salute the USA.  If we were lucky, some passers-by would honk their horn at us.  I always thought that was the coolest.