Excel sheet-How to increment numbers in the row which is composed of text

First, let me explain the appearance of my data
consider the following in different row on a single column(cell only)
A1:
x
y
z
–
–
i wanted to prefix a number with the text
say
A1.
1.x
2.y
in one column cell only
Question here is
if i have n no of text rows here for a single column
and i have to increment only the no
say after 1.x
how can i prefix or increment no in each cell
,text should not be changed?