How to see both sides of transparrent mesh?

  Shader "Transparent/Cutout/DiffuseCullOff" {
  Properties {
      _Color ("Main Color", Color) = (1,1,1,1)
      _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
      _Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
  }
  
  SubShader {
      Tags {"Queue"="AlphaTest" "IgnoreProjector"="True" "RenderType"="TransparentCutout"}
      LOD 200
      Cull Off
      
  CGPROGRAM
  #pragma surface surf Lambert alphatest:_Cutoff
  
  sampler2D _MainTex;
  fixed4 _Color;
  
  struct Input {
      float2 uv_MainTex;
  };
  
  void surf (Input IN, inout SurfaceOutput o) {
      fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
      o.Albedo = c.rgb;
      o.Alpha = c.a;
  }
  ENDCG
  }
  
  Fallback "Transparent/Cutout/VertexLit"
  }

The "Cull" function in a shader can be used to stop backwards facing faces from being rendered as it usually good for optimisation, but changing it to Cull Off it will render both sides :)

Just save this as a shader and apply this one to the material