  Among the supernovae (SNe) that show strong interaction with the
circumstellar medium, there is a rare subclass of Type Ia supernovae, SNe
Ia-CSM, that show strong narrow hydrogen emission lines much like SNe IIn but
on top of a diluted over-luminous Type Ia spectrum. In the only previous
systematic study of this class (Silverman et al. 2013), 16 objects were
identified, 8 historic and 8 from the Palomar Transient Factory (PTF). Now
using the successor survey to PTF, the Zwicky Transient Facility (ZTF), we have
classified 12 additional objects of this type through the systematic Bright
Transient Survey (BTS). In this study, we present and analyze the optical and
mid-IR light curves, optical spectra, and host galaxy properties of this
sample. Consistent with previous studies, we find the objects to have slowly
evolving light curves compared to normal SNe Ia with peak absolute magnitudes
between -19.1 and -21, spectra having weak H$\beta$, large Balmer decrements of
~7 and strong Ca NIR emission. Out of 10 SNe from our sample observed by
NEOWISE, 9 have $3\sigma$ detections, along with some showing a clear reduction
in red-wing of H$\alpha$, indicative of newly formed dust. We do not find our
SN Ia-CSM sample to have a significantly different distribution of equivalent
width of He I $\lambda5876$ than SNe IIn as observed in Silverman et al. 2013.
The hosts tend to be late-type galaxies with recent star formation. We also
derive a rate estimate of 29$^{+27}_{-21}$ Gpc$^{-3}$ yr$^{-1}$ for SNe Ia-CSM
which is ~0.02--0.2 % of the SN Ia rate. This work nearly doubles the sample of
well-studied Ia-CSM objects in Silverman et al. 2013, increasing the total
number to 28.
