Let μ be a Borel probability measure with compact support on
R
d
. We say that μ is a spectral measure if there exists
Λ
⊆
R
d
, called a spectrum of μ, such that
E
(
Λ
)
≔
{
e
−
2
π
i
⟨
λ
,
x
⟩
}
λ
∈
Λ
forms an orthonormal basis for L
2(μ). In this paper, we study the structure of spectra for a class of self-similar spectral measure μ
R,B
with product form on
R
. We first give a partially characterize for E
Λ to be a maximal orthogonal family in L
2(μ
R,B
) by using the notion of maximal tree mapping. Based on this, we give a sufficient condition for a maximal orthogonal family E
Λ (which corresponds to a maximal tree mapping) to be an orthonormal basis of L
2(μ
R,B
). Moreover, we completely settle two types of spectral eigenvalue problems for μ
R,B
. Precisely, on the first case, for the model spectrum (simplest spectrum) of μ
R,B
, we characterize all possible real numbers t such that tΛ is also a spectrum of μ
R,B
. On the other case, we characterize all possible real numbers t such that there exists a countable set Λ such that Λ and tΛ are both spectra of μ
R,B
.