Can't apply push transition between two sequences

Hello, friends!

I'm trying to apply the push effect transition, between two sequences. There are sequence 1 and sequence 2. I've just opened the third sequence, copy and pasted sequence 1 and 2 on it. Now I'm trying to apply the effect, but I can't do it. The program let me apply the effect just in one of the sequences, but not between them for sequence 1 push sequence 2. How can I do it?