parent child extension

How many rows are in your starting table?  I have a solution but it gets very slow if the number of rows is large.  For 2000 rows (and up to ten deep Child levels) it takes about 45 seconds to run.  If your starting table is a lot larger it is probably too slow.

let
    fx_Recur = (x as text, l as list) =>
        let lst = {Text.Upper(x)} & l in try Fx_Recur(Text.Upper(Prt{List.PositionOf(Chd, x, Occurrence.First, Comparer.OrdinalIgnoreCase)}), lst) otherwise lst,

    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCk4tUXBU0lEqLk1KLC6uNFSK1YlWKoYKpmXmlKQWoQgl5VdA+DD1OkrBEKYRunhOYlJqDrKgEcie5KLUcnTBpPycEqXYWAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Parent = _t, Child = _t]),
    Prt = Source[Parent],
    Chd = Source[Child],
    Hierarchy = Table.AddColumn(Source, "h", each fx_Recur([Parent], {Text.Upper([Child])})),
    #"Selected Rows" = Table.SelectRows(Hierarchy, each not List.Contains(Prt, [Child], Comparer.OrdinalIgnoreCase))[h],
    Expanded = Table.Combine(List.Transform(#"Selected Rows", each Table.FromRows({_})))
in
    Expanded

This might take 2 to 6 hours on 120000 rows.  Start it before leaving work for the day and it should be done when you return.

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    tbl = Table.Buffer(Table.RenameColumns(Source,{{"Child", "Child level 1"}})),
    chld = List.Buffer(tbl[Child level 1]),
    nokids = Table.SelectRows(tbl, each not List.Contains(chld, [Parent] )),
    haskids = Table.Buffer(Table.SelectRows(tbl, each List.Contains(chld, [Parent] ))),

    lsta = List.Accumulate({1..12}, {nokids, #table({"Parent","Child level 1"}, {})}, (s,c)=>
            let 
                lastcol = List.Last(Table.ColumnNames(s{0})),
                ct = List.Count(List.RemoveNulls(Table.Column(s{0},lastcol)))
            in   
                if ct>0 then  
                    let  
                        tbl1 =Table.NestedJoin(s{0}, {"Child level " & Text.From(c)}, haskids, {"Parent"}, "Child level " & Text.From(c+1)),
                        tbl1e = Table.ExpandTableColumn(tbl1, "Child level " & Text.From(c+1), {"Child level 1"}, {"Child level " & Text.From(c+1)}),
                        tbl1k = Table.SelectRows(tbl1e, each Record.Field(_, "Child level " & Text.From(c+1)) <> null)
                    in   
                        {tbl1k, s{1} & Table.SelectRows(tbl1e, each Record.Field(_, "Child level " & Text.From(c+1)) = null)}
                else s),
    tbla = lsta{0} & lsta{1}
in
    tbla