b-tree bbbbbb beebee beefer beeter befree befret berbee berber bereet berere berrer berret bertre betere betete bettee better breefe breere brette ebbert eebree effere effete efreet efter- erbree errett ferber ferfer ferrer ferret fertee ferter fetter frefre frette fterer fterre r-tree reefer reeffe refeet refeff refert refete refret refter reteer reteet retere retree retret retter t-tree teebee teetee teeter terete terrer terret terter tertre tetete tetter treete trefet trefte tretee trette