tikz-graph último nivel del árbol solo rodeado por un círculo

Question

¿Cómo puedo tener en un círculo solo el último nivel (hojas) del árbol (no todos)?

\documentclass[tikz,border=10pt]{standalone}

\usetikzlibrary{graphdrawing}
\usetikzlibrary{graphs}
\usegdlibrary{trees}
\begin{document}

\tikzset{ every node/.style={circle, draw, fill=gray!10,, minimum size=0.75cm} }

\begin{tikzpicture}[>=stealth]

\graph [tree layout, grow=down, fresh nodes, level distance=0.5in, sibling distance=0.5in]
    {
        200 -> { 
          5 -> { 2, 2.5 },
         40 -> { 5 -> {2, 2.5 }, 8->{2,4} } 
        } 
    };
\end{tikzpicture}
\end{document}

Answer 1

En lugar de aplicar el estilo a every node, cree un nuevo estilo circnodeque aplique solo a los nodos seleccionados.

Alternativamente, podría considerar usarlo forestdonde sea realmente fácil.

\RequirePackage{luatex85}
\documentclass[tikz,border=10pt]{standalone}
\usepackage{forest}

\usetikzlibrary{graphdrawing}
\usetikzlibrary{graphs}
\usegdlibrary{trees}
\begin{document}

\tikzset{ circnode/.style={circle, draw, fill=gray!10,, minimum size=0.75cm} }

\begin{tikzpicture}[>=stealth]

\graph [tree layout, grow=down, fresh nodes, level distance=0.5in, sibling distance=0.5in]
    {
        200 -> { 
          5 -> { 2 [circnode], 2.5 [circnode]},
         40 -> { 5 -> {2[circnode], 2.5[circnode] }, 8->{2[circnode],4[circnode]} } 
        } 
    };
\end{tikzpicture}

\begin{forest}
for tree={l=0.5in,s sep=5mm,edge={-stealth}},
where n children=0{circnode}{}
[200
  [5
    [2][2.5]
  ]
  [40
    [5
      [2][2.5]
    ]
    [8
      [2][4]
    ]
  ]
]
\end{forest}
\end{document}

Answer 2

También me topé con esta solución antes de leer Torbjorn, T.

\tikzstyle{leaves}=[circle, draw, fill=gray!10, minimum size=0.75cm]

\begin{tikzpicture}[>=stealth]

\graph [tree layout, grow=down, fresh nodes, level distance=0.5in, sibling distance=0.5in]
{
    200 -> { 
      5 -> { 2[leaves], 2.5[leaves] },
     40 -> { 5 -> {2[leaves], 2.5[leaves] }, 8-> {2[leaves],4[leaves]} }
    } 
};
\end{tikzpicture}