代码

digraph Forest {
    node [fontname="Arial", shape=circle, style=filled, color="#ffffff", fillcolor="#0077be", fontsize=12, width=0.5, height=0.5];
    edge [fontname="Arial", fontsize=10, color="#333333", arrowsize=0.5];

    // 定义树1的节点
    node1 [label="A"];
    node2 [label="B"];
    node3 [label="C"];
    node4 [label="D"];

    // 定义树2的节点
    node5 [label="E"];
    node6 [label="F"];
    node7 [label="G"];

    // 定义树3的节点
    node8 [label="H"];
    node9 [label="I"];
    node10 [label="J"];

    // 连接树1的节点
    node1 -> node2;
    node1 -> node3;
    node2 -> node4;

    // 连接树2的节点
    node5 -> node6;
    node5 -> node7;

    // 连接树3的节点
    node8 -> node9;
    node8 -> node10;
}

效果