6 year old boy wants to dress like a girl

My 6 year old has always been interested in all "boy" things, he likes to play in the dirt, ride his 4-wheeler, play with cars, etc. I've offered "girl" things when he was younger just to be fair. He's just never been interested in "girl" things, until we went to Walt Disney world when he was 4. He wanted to use his 1 fast pass to see Elsa, which I found totally fine and was excited for him. No other interests in "girl" stuff had occured.

Fast forward to about a month ago, I found him hiding under my bed with all my hair extensions. I wrote it off as him trying to sleep with my hair to feel closer to me since I started working full time again and we moved to our new home, which took alot of our time. This week I was cleaning his room and discovered my hair extensions, high heels, a dress, my lacy underwear, and my bra. I confronted him about them being under his bed and he finally admitted he likes to dress like a girl after he goes to bed at night.

I handled this the best I could and didn't scold him, but I didn't encourage it either. I pretty much told him that I love him and he didn't need to hide anything from me.

Present day, he asked me if I was going to buy brown hair extensions... I just told him I didn't plan on buying any since I wanted my hair to be blonde.

Help... I don't know what to do. I'm not against gays or transgender, but I just don't know what to do or how to handle this. I think my next step is to see a child psychiatrist, but I've never liked psychiatrists and I've had bad experiences with them in the past. I want my son to know I love him and will be there for him no matter what, but I really don't want to encourage him to continue this behavior.