\documentclass[landscape]{article}
\usepackage[margin=.5in]{geometry}
\usepackage[linguistics]{forest}
\usetikzlibrary{positioning}
\usepackage{amsmath}
\usepackage{gb4e,cgloss}
\def\1{$'$}
\def\uD{$u$D}
\newcommand{\TR}[1]{$\langle\text{#1}\rangle$}
\forestset{default preamble={for tree={inner sep=1pt,edge path'/.append={very thick}}},
expand/.style={s sep=#1},
blue roof/.style={edge path'={%
[blue](.parent first)--(!u.children)--(.parent last)--cycle
}
},}
\tikzset{red arrow/.style={->,red},every picture/.style={line width=2pt}}