Block Randomization from Two Distinct Groups

I would like to use randomization in my study, but am a bit stuck when it comes to the specifics:
I have 20 blocks that are split into 2 groups of 10. I would like participants to view 5 blocks from group 1 and 5 blocks from group 2 randomly. Participants would see 10 blocks in total. In other words, I would like the order of the blocks they see to be randomly chosen from each group and mixed together. So, they may see a block from group 1 and then group 2, for example, until they have seen 5 from each group.
The trouble I'm having is that I don't want the two groups grouped into a single group as I want to have the same amount of blocks shown from each group. Currently, participants will see 5 random blocks from group 1 and then 5 random blocks from group 2. Ideally, I would have the blocks they see be mixed up.
I would greatly appreciate some help! :)