Unable to get a field of linked doctype in 'fetch from' options while defining a doctype

[Vinay1]

when creating a new ‘asset data’, for the doctype field ‘ward’ only those values should be displayed which belongs to the branch

ie., acoording to above image, only those wards which are present in DKR branch should be displayed

so i tried to add the wards field of branch doctype in fetch from options but wards field of branch is not showing in fetch from options

here is the DKR branch doctype record

here is the Branch doctype

here is the Asset data doctype

here is the Wards per Branch doctype

Am I doing it correct or Is there any other way of doing it