Vertical dots in a tree with forest

I am writing a paper about the collatz conjecture, and I want to show a diagram, but I don’t know how to add ellipses to the tree.

usepackage{forest}

begin{forest} for tree={
    edge path={noexpandpath[forestoption{edge}] (forestOve{forestove{@parent}}{name}.parent anchor) -- +(0,-12pt)-| (forestove{name}.child anchor)forestoption{edge label};}
}

[1
    [2
        [4
            [8
                [16
                    [32
                        [64
                            [128
                                [256]
                            ]
                            [21
                                [42]
                            ]
                        ]
                    ]
                    [5
                        [10
                            [20
                                [40]
                            ]
                            [3
                                [6]
                            ]
                        ]
                    ]
                ]
            ]
        ]
    ]
]

end{forest}

I want the ellipses to be where the red rectangles are, if possible

documentclass{article}
usepackage{forest}
begin{document}
begin{forest}
for tree={math content,align=center}
[1
    [2
        [4
            [8
                [16
                    [32
                        [64
                            [128
                                [256vdots]
                            ]
                            [21
                                [42vdots]
                            ]
                        ]
                    ]
                    [5
                        [10
                            [20
                                [40vdots]
                            ]
                            [3
                                [6vdots]
                            ]
                        ]
                    ]
                ]
            ]
        ]
    ]
]
end{forest}

end{document}