documentclass[12pt]{article}
usepackage{setspace,amsmath,graphicx,float}
usepackage[english]{babel}
usepackage[natbibapa]{apacite}
usepackage{times}
usepackage{tikz}
usetikzlibrary{shapes,arrows,arrows.meta,positioning,calc}
begin{document}
begin{figure}[H]
centering
tikzstyle{block} = [draw, rectangle, minimum height=5.5em, minimum width=19em]
tikzstyle{smallblock} = [draw, rectangle, minimum height=5.5em, minimum width=9em]
tikzstyle{input} = [coordinate]
tikzstyle{output} = [coordinate]
tikzstyle{pinstyle} = [pin edge={to-,thin,black}]
begin{tikzpicture}[auto,node distance=7cm,>=latex',align=center]
    node [input, name=input] {};
    node [block, rounded corners=5pt, right of=input] (A) {Start with the narrowest product\ or geographic market definition.};
    node [block, rounded corners=5pt, below of=A, node distance=3.5cm] (B) {Is it profitable for a monopoly producer of\ that product to increase prices in a small but\ significant and nontransitory way?};
    node [block, rounded corners=5pt, below of=B, node distance=3.5cm] (C) {There must be at least one good substitute\ excluded from the current market definition.\ Expand the market to include it.};
    node [block, rounded corners=5pt, below of=C, node distance=3.5cm] (D) {Now have a multiproduct monopolist.\ Could he profitably raise prices?};
    node [smallblock, rounded corners=5pt, right of=D, node distance=8cm] (E) {Stop.\ Market definition\ is wide enough.};
    draw [-{Latex[length=3mm]}] (A) -- node[auto][name=1] [right]{} (B);
    draw [-{Latex[length=3mm]}] (B) -- node[auto][name=2] [right]{No} (C);
    draw [-{Latex[length=3mm]}] (C) -- node[auto][name=3] [right]{} (D);
    draw [-{Latex[length=3mm]}] (D) -- node[auto][name=4] [above]{Yes} (E);
    draw [-{Latex[length=3mm]}] (B) -| node[near start][name=5] [above]{Yes} (E);
    draw [-{Latex[length=3mm]}] (D) -- +(0,1)|- node[auto][name=6] [left]{No} (C);
end{tikzpicture}
caption[Illustration of an HMT decision tree]{Illustration of an HMT decision tree citep{QuantTech}.}label{AlgorithmHMT}
end{figure}
end{document}

documentclass[12pt]{article}
usepackage{setspace,amsmath,graphicx,float}
usepackage[english]{babel}
usepackage[natbibapa]{apacite}
usepackage{times}
usepackage{tikz}
usetikzlibrary{arrows, arrows.meta, calc, positioning, quotes, shapes}

begin{document}
begin{figure}
centering
    begin{tikzpicture}[
    auto,
    node distance = 11mm and 22mm,
      base/.style = {draw, rounded corners=5pt, minimum height=5.5em,
                     align=center},
     block/.style = {base, minimum width=19em},
smallblock/.style = {base, minimum width=9em},
                        ]
coordinate (in);
node [block,right=of in] (A) {Start with the narrowest product\
                               or geographic market definition.};
node [block,below=of A ] (B) {Is it profitable for a monopoly producer of\
                               that product to increase prices in a small but\
                               significant and nontransitory way?};
node [block,below=of B ] (C) {There must be at least one good substitute\
                               excluded from the current market definition.\
                               Expand the market to include it.};
node [block,below=of C ] (D) {Now have a multiproduct monopolist.\
                               Could he profitably raise prices?};
node [smallblock,right=of D] (E) {Stop.\
                                   Market definition\
                                   is wide enough.};
draw [-{Latex[length=3mm]}]
    (A) edge                    (B)
    (B) edge ["No"]             (C)
    (C) edge                    (D)
    (D) edge ["Yes"]            (E);
draw [-{Latex[length=3mm]}]
    (B) -| node[pos=0.25,name=5] {Yes} (E);
draw [-{Latex[length=3mm]}]
    (D.west) -- +(-1,0) |- node[pos=0.25] {No} (C);
    end{tikzpicture}
caption[Illustration of an HMT decision tree]
        {Illustration of an HMT decision tree citep{QuantTech}.}
    label{AlgorithmHMT}
end{figure}
end{document}