[ Tree (Cell 1:1 1:7 (NodeHeader (HeaderSection 1))) 
    [ Tree (Cell 1:3 1:7 NodePara) 
        [ Tree (Cell 1:3 1:7 (NodeToken (TokenText "sec1"))) []
        ] 
    ] 
, Tree (Cell 2:1 3:9 (NodeHeader (HeaderSection 1))) 
    [ Tree (Cell 2:3 2:7 NodePara) 
        [ Tree (Cell 2:3 2:7 (NodeToken (TokenText "sec2"))) []
        ] 
    , Tree (Cell 3:1 3:9 (NodeHeader (HeaderSection 2))) 
        [ Tree (Cell 3:4 3:9 NodePara) 
            [ Tree (Cell 3:4 3:9 (NodeToken (TokenText "sec21"))) []
            ] 
        ] 
    ] 
]