Creating groups based on numbers

Select the table/query in question. Hit "Edit Queries".

In there, you have option to add blank query. Do so and go to Advanced Editor.

Paste in "M" as below (you can adjust range as needed or add more arugments).

(vals) =>
let ValBucket =
    {
        {(x)=>x<10, "0-9 members"},
        {(x)=>x<25, "10-24 members"},
        {(x)=>x<50, "25-49 members"},
        {(x)=>true, "50+ members"}
    },
    Result = List.First(List.Select(ValBucket, each _{0}(vals))){1}
in
    Result

Once confirmed, rename the query to something that makes sense (Ex. BucketFunc).

Now, still in Query Editor, go back to your table where you want to add custom buckets/bands.

In "Add column" ribbon tool, select "Invoke Custom Function".

Choose a name for the column and select "BucketFunc" you just created. "vals" should be column where the values you want to band belongs.

Result should look like below.

aksl,

You could also use DAX to add a calculated column.

Group Name =
SWITCH (
    TRUE (),
    Table1[column X] >= 0
        && Table1[column X] <= 9, "0-9 members",
    Table1[column X] >= 10
        && Table1[column X] <= 24, "10-24 members",
    "other"
)