Data Transformation unpivoting for multiple headers

Whoever created that input format should be led behind the shed for a friendly discussion with a clue-by-four.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WUlDSgeOAABxEaDhuMlYnWskjNTEltUjBECgEZRohmMZApqGRroGFrpGBkQmIY4zMMUHmmCJzzJA5lBkAcqRPfnJiSWZ+HtiZjk5gx3qASJBakHtNocFgjMQGYUMwjWKEEdgIsCc9jKDKjKBGwbSaQrUaw41BMcIYbIQx2AhjqDJzJJcYQmkzILaAGmGmFBsLAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t, Column2 = _t, Column3 = _t, Column4 = _t, Column5 = _t, Column6 = _t, Column7 = _t, Column8 = _t, Column9 = _t, Column10 = _t, Column11 = _t, Column12 = _t, Column13 = _t]),
    Table = Table.AddIndexColumn(Table.PromoteHeaders(Table.Skip(Table.SelectColumns(Source,{"Column1", "Column2", "Column3"}),1), [PromoteAllScalars=true]), "Index", 0, 1, Int64.Type),
    #"Removed Columns" = Table.RemoveColumns(Source,{"Column1", "Column2", "Column3"}),
    #"Added Index" = Table.AddIndexColumn(#"Removed Columns", "Index", -2, 1, Int64.Type),
    #"Unpivoted Other Columns" = Table.UnpivotOtherColumns(#"Added Index", {"Index"}, "Attribute", "Value"),
    #"Added Custom" = Table.AddColumn(#"Unpivoted Other Columns", "Date", (k)=> Table.SelectRows(#"Unpivoted Other Columns",each [Attribute]=k[Attribute] and [Index]=-1)[Value]{0}, type date),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Category", (k)=> Table.SelectRows(#"Unpivoted Other Columns",each [Attribute]=k[Attribute] and [Index]=-2)[Value]{0},type text),
    #"Filtered Rows" = Table.SelectRows(#"Added Custom1", each ([Index] <> -2 and [Index] <> -1)),
    #"Removed Columns1" = Table.RemoveColumns(#"Filtered Rows",{"Attribute"}),
    #"Pivoted Column" = Table.Pivot(#"Removed Columns1", List.Distinct(#"Removed Columns1"[Category]), "Category", "Value"),
    #"Merged Queries" = Table.NestedJoin(Table, {"Index"},#"Pivoted Column", {"Index"},  "Table", JoinKind.Inner),
    #"Expanded Table" = Table.ExpandTableColumn(#"Merged Queries", "Table", {"Date", "PP", "UWP"}, {"Date", "PP", "UWP"}),
    #"Removed Columns2" = Table.RemoveColumns(#"Expanded Table",{"Index"})
in
    #"Removed Columns2"

How to use this code: Create a new Blank Query. Click on "Advanced Editor". Replace the code in the window with the code provided here. Click "Done". Once you examined the code, replace the Source step with your own source.