documentclass[border=5mm]{standalone}

usepackage{tikz}

usetikzlibrary{matrix}
usetikzlibrary{positioning}

newcommand{listbcs}[4]{
    tikzset{
        barycentric setup/.code={foreach X [count=Y] in {#1}
            {ifnumY=1
                    xdefbaryarg{X=1}
                else
                    xdefbaryarg{baryarg,X=1}
                fi}},
        barycentric list/.style={barycentric setup={#1},insert path={%
                (barycentric cs:baryarg)}}
    }
    path[barycentric list={#1}] node[anchor=center,align=flush center,#2] (#3) {#4};
}

newcommand{multilinks}[4]{%
    begin{scope}[x=1em,y=1em]
        listbcs{#2}{}{bcright}{}
        newdimenxright
        newdimenybc
        newdimendump
        path(bcright);
        pgfgetlastxy{dump}{ybc}
        path(-1,0);
        newdimenxtemp
        pgfgetlastxy{xtemp}{dump}
        foreach ver in {#2}{
            newdimenxnow
            path(ver.west);
            pgfgetlastxy{xnow}{dump}
            ifdimxnow<xtemp
                path(ver.west);
                pgfgetlastxy{xtemp}{dump}
        }
        coordinate (midright) at ({xtemp-#3 em},ybc);
        coordinate (midleft) at ({xtemp-#3 em-#4 em},ybc);
        foreach i in {#1} {
            foreach j in {#2}{
                newdimenystart
                path (i.east);
                pgfgetlastxy{dump}{ystart}
                newdimenymid
                path (midleft);
                path (midright);
                pgfgetlastxy{dump}{ymid}
                newdimenyend
                path (j.west);
                pgfgetlastxy{dump}{yend}
                ifdimystart=ymidrelax%
                    ifdimymid=yendrelax%
                        draw[->] (i.east)--(j.west);%
                    else%
                        draw[->,rounded corners] (i.east)--(midright)--(j.west);%
                    fi%
                else%
                    ifdimymid=yendrelax%
                        draw[->] (i.east)--(midleft)--(j.west);%
                    else%
                        draw[->,rounded corners] (i.east)--(midleft)--(midright)--(j.west);%
                    fi%
                fi%
            }
        }
    end{scope}
}

begin{document}
    tikzset{
        basic/.style={
            draw,
            rounded corners=2pt,
            thick,
            text width=8em,
            align=flush center,
            node distance=2em
        }
    }
    begin{tikzpicture}
        matrix[row sep=2em, column sep=4em, every node/.style={basic}] {
            node(a){text}; & node(c){text}; \
            node(b){text}; & node(d){text}; \
            node(e){text}; & node(f){text}; \
        };
        multilinks{b,e}{d,f}{1}{1}
    end{tikzpicture}
end{document}