\usetikzlibrary{decorations.growingwave}
\tikzset{
  small squiggly line fade in/.style={
    -,% No arrow head
    shorten >=0pt,%%%%%%%%%%%%%%%%%%%%%%%%%
    decorate,
    decoration={
      growth wave,
      growth start size=0pt,
      growth end size=-1pt,%{-1pt,-1pt,0pt},%%%%%%%%%
      % growth end steps={0.6,.7},
      %growth end steps={0.2,0.6,1},%%%%%%%%
      growth wave length=1pt,%{1pt,1pt,1pt},%%%%%
      growth cosine,
      % pre length=5mm,
      post length=0mm,%%%%%%%%%%%%%%%%%%%%%%
    },
  },
  small squiggly line no fade/.style={
    -,% No arrow head
    shorten >=0pt,%%%%%%%%%%%%%%%%%%%%%%%%%
    decorate,
    decoration={
      growth wave,
      growth start size=-1pt,
      growth end size=-1pt,%{-1pt,-1pt,0pt},%%%%%%%%%
      % growth end steps={0.6,.7},
      % growth end steps={0.2,0.6,1},
      growth wave length=1pt,%{1pt,1pt,1pt},%%%%%
      growth cosine,
      pre length=1pt,%%%%%%%%%%%%%%%%
      post length=1pt,%%%%%%%%%%%%%%%%%%%%%%
    },
  },
  squiggly line/.style={
    -,% No arrow head
    shorten >=0pt,%%%%%%%%%%%%%%%%%%%%%%%%%
    decorate,
    decoration={
      growth wave,
      growth start size=0pt,
      growth end size=2pt,%{3pt,0pt},
      % growth end steps={0.6,.7},
      % growth end steps={0.8,1},
      growth wave length=2pt,%{2pt,1pt},
      growth cosine,
      % pre length=5mm,
      post length=0mm%%%%%%%%%%%%%%%%%%%%%%
    },
  },
  squiggly arrow/.style={
    ->,
    shorten >=1.5pt,
    decorate,
    decoration={
      growth wave,
      growth start size=0pt,
      growth end size=2pt,%{3pt,0pt},
      % growth end steps={0.6,.7},
      % growth end steps={0.8,1},
      growth wave length=2pt,%{2pt,1pt},
      growth cosine,
      % pre length=5mm,
      post length=2mm
    },
  },
}

\tikzset{
  /forest/.cd, % Set forest styles
  start squiggly tree/.style={
    for children={
      edge={small squiggly line fade in,},
      continue squiggly tree,
    }
  },
  continue squiggly tree/.style={
    for children={
      edge={small squiggly line no fade,},
      continue squiggly tree,
    }
  }
}
