digraph {

size=6.25;
rankdir=TB
//splines = ortho;
ranksep = 0.2;
nodesep = 0.3;

edge [ penwidth = 1.75, fontname="Sans" ]
node [ penwidth = 1.75, shape = "box", fontname="Sans", ]
graph [ penwidth = 1.75, fontname="Sans" ]

{
    node [ shape = "none" ];
    txids [ label = "Row 1: Transaction hashes (TXIDs)\n(A is coinbase; C can spend output from B)" ];
    row2  [ label = "Row 2: Hashes of paired TXIDs" ];
    rootrow [ label = "Merkle root" ];

    txids -> row2 -> rootrow [ style = "invis" ];
}

txid_a [ label = "A" ];
txid_b [ label = "B" ];
txid_invis [ label = "C", style = "invis" ];
txid_c [ label = "C" ];

row2_ab [ label = "H(A|B)" ];
row2_cc [ label = "H(C|C)" ];

root [ label = "H(H(A|B)|H(C|C))" ];

txid_a -> row2_ab [ weight = 1 ];
txid_b -> row2_ab [ weight = 1 ];
txid_c -> row2_cc;
txid_invis -> row2_cc [ style = "invis" ];

row2_ab -> root;
row2_cc -> root;


label = "\n Example Merkle Tree Construction  [Hash function H() = SHA256(SHA256())]"
}