To cite package ‘TreeTools’ in publications use:

  Smith (2019). TreeTools: create, modify and analyse phylogenetic
  trees. Comprehensive R Archive Network. doi: 10.5281/zenodo.3522725

A BibTeX entry for LaTeX users is

  @Manual{Smith2019,
    title = {TreeTools: create, modify and analyse phylogenetic trees},
    author = {Martin R. Smith},
    note = {R package version 1.12.0},
    year = {2019},
    doi = {10.5281/zenodo.3522725},
    organization = {Comprehensive R Archive Network},
  }