Count frequencies of (binary) variable and merge these to original dataset

The following provides one solution to the problem. However, it seems unnecessarily complicated to me. I would appreciate if fellow Stata users could suggest a simplification.
The dataset is the following:

ID	communityID	treat
1	1	1
2	1	1
3	1	0
4	1	1
5	2	0
6	2	1

Where I count the frequencies of (positive) treatment per group. I add these frequencies (treat==1) as a new variable (which is equal within each communityID).

preserve
contract communityID treat, zero nomiss
drop if treat==0 // IN ORDER TO HAVE m:1 MERGE
save treat.dta, replace
restore
merge m:1 communityID using treat.dta

The resulting data NRPS.dta then contains the collapsed information

communityID	treat	_freq
1	1	3
1	0	1
2	1	1
2	0	1

What is the best way of solving this problem without saving and merging data?