discrete mathematics – How do I do a runtime analysis on a multipart recurrence relation

If I have a recurrence relationship like this: T(n) = T(n/5) + T(4n/5) + Θ(n), how would I do a runtime analysis? I believe I can’t use a master theorem. I tried to draw a tree but some of the branches terminate earlier. There’s a way to calculate the big-O notation by assuming T(n) <= 2 T(4n/5). But is it Θ as well?