To cite irtrees in publications use:

De Boeck P, Partchev I (2012). “IRTrees: Tree-Based Item Response Models of the GLMM Family.” Journal of Statistical Software – Code Snippets, 48(1), 1–28. https://www.jstatsoft.org/v48/c01/.

Corresponding BibTeX entry:

  @Article{,
    title = {IRTrees: Tree-Based Item Response Models of the GLMM
      Family},
    author = {Paul {De Boeck} and Ivailo Partchev},
    journal = {Journal of Statistical Software -- Code Snippets},
    year = {2012},
    volume = {48},
    number = {1},
    pages = {1--28},
    url = {https://www.jstatsoft.org/v48/c01/},
  }