Hi these are "American Hornbeam" used for the columnar growth habit,. Columnar describes a growth habit more compact and straight like a column. Theres pyramidal, spreading, irregular round,, others.
Columnar trees look great lining a path in a formal landscape, don't take up as much space as other trees too,. There are other varieties of columnar trees such as the popular "upright English oak" or Fagus verticulata.
thanks for the question.
Todd Nappi

Thank you